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Prevalence and determinants of pain in spinal cord injury during initial inpatient rehabilitation: data from the Dutch spinal cord injury database

  • Tim C. Crul
    Affiliations
    Centre of Excellence for Rehabilitation Medicine, UMC Utrecht Brain Centre, University Medical Centre Utrecht, and De Hoogstraat Rehabilitation, Utrecht, The Netherlands
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  • Marcel W.M. Post
    Affiliations
    Centre of Excellence for Rehabilitation Medicine, UMC Utrecht Brain Centre, University Medical Centre Utrecht, and De Hoogstraat Rehabilitation, Utrecht, The Netherlands

    University of Groningen, University Medical Centre Groningen, Centre for Rehabilitation, Groningen, The Netherlands
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  • Johanna M.A. Visser-Meily
    Affiliations
    Centre of Excellence for Rehabilitation Medicine, UMC Utrecht Brain Centre, University Medical Centre Utrecht, and De Hoogstraat Rehabilitation, Utrecht, The Netherlands

    Department of Rehabilitation, Physical Therapy Science & Sports, UMC Utrecht Brain Center, University Medical Center Utrecht, Utrecht, The Netherlands
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  • Janneke M. Stolwijk-Swüste
    Correspondence
    Corresponding author: J. Stolwijk, Rembrandtkade 10, 3583 TM, Utrecht, the Netherlands, +31 30 256 1211
    Affiliations
    Centre of Excellence for Rehabilitation Medicine, UMC Utrecht Brain Centre, University Medical Centre Utrecht, and De Hoogstraat Rehabilitation, Utrecht, The Netherlands

    Department of Spinal Cord Injury and Orthopedics, De Hoogstraat Rehabilitation, Utrecht, The Netherlands
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Open AccessPublished:July 29, 2022DOI:https://doi.org/10.1016/j.apmr.2022.07.005

      Objective

      To describe the prevalence and characteristics of spinal cord injury (SCI) related pain during initial inpatient rehabilitation and to investigate relationships with demographic and lesion characteristics.

      Design

      Cohort during inpatient rehabilitation.

      Setting

      Eight specialized SCI rehabilitation centers in the Netherlands.

      Participants

      Patients with newly acquired SCI admitted for inpatient rehabilitation between November 2013 and August 2019.

      Interventions

      Not applicable.

      Main Outcome Measures

      Presence of pain at admission and discharge. Logistic regression analyses were used to study the prevalence of pain related to sex, age, etiology, completeness and level of injury.

      Results

      Data from 1432 patients were available. Of these patients 64.6% were male, mean age was 56.8 years, 59.9% had a non-traumatic SCI, 63.9% were classified as ASIA impairment scale (AIS) D and 56.5% were paraplegic. Prevalence of pain was 61.2% at admission (40.6% nociceptive pain (NocP), 30.2% neuropathic pain (NeuP) and 5.4% other pain) and 51.5% at discharge (26.0% NocP, 31.4% NeuP and 5.7% other pain). Having NocP at admission was associated with traumatic SCI. AIS B had a lower risk of NocP compared to AIS D at admission. Having NocP at discharge was associated with female sex and traumatic SCI. AIS C compared to AIS D had a lower risk of NocP at discharge. Having NeuP at admission was associated with female sex. Having NeuP at discharge was associated with female sex, age <65 vs >75 and tetraplegia.

      Conclusion

      SCI-related pain is highly prevalent during inpatient rehabilitation. Prevalence of NocP decreased during inpatient rehabilitation and prevalence of NeuP stayed the same. Different patient and lesion characteristics were related to the presence of SCI-related pain. Healthcare professionals should be aware of these differences in screening patients on presence and development of pain during inpatient rehabilitation.

      Key words

      Spinal cord injury (SCI) results in varying degrees of function loss distal to the level of the injury[1]. Besides motor and sensory function loss, SCI is often accompanied by secondary conditions that affect quality of life[2,3]. Pain is one of the secondary conditions that is frequently reported by patients with SCI. The prevalence of SCI-related pain is estimated at 61%, with a large amount of heterogeneity in studies. Pain is one of the most challenging symptoms to manage[4]. The prognosis of SCI-related pain is poor with many patients reporting the pain to remain the same or even worsen over time[5]. In addition, SCI-related pain is known to have a severe negative impact on quality of life[2,6].
      SCI-related pain is classified by The International Association of the Study of Pain into two main types: nociceptive pain (NocP) and neuropathic pain (NeuP) [5]. Nociceptive pain is caused by tissue damage[2,6], and is divided in two main categories: musculoskeletal pain and visceral pain[7]. Examples for musculoskeletal pain include pain resulting from joint arthritis, spinal fractures, muscle injury, rotator cuff tendinopathy and muscle spasms[7]. Examples for causes of visceral pain are constipation, urinary tract infection, ureteral calculus and bowel impaction[7]. Neuropathic pain is caused by damage or dysfunction of the nervous system[8,9]. In SCI, NeuP can be located above, at or below level of injury[2]. Pain above level of the injury is often not due to the SCI itself, but caused by concomitant compression neuropathy or by regional pain syndromes[2]. Pain at level of the injury can be caused by damage or disease of the nerve root or spinal cord[2,7]. Pain below level of the injury is caused directly by injury of the spinal cord[2,7].
      The treatment of SCI-related pain remains a challenge[10–12]. Pharmacological treatment strategy for NocP is based on the stepped care of paracetamol, non-systemic anti-inflammatory drugs and opioids in accordance with the World Health Organization Cancer Pain Relief[13,14]. For NeuP, pregabalin and gabapentin are the most evidence based treatment options and have shown a significant reduction in pain intensity in multiple studies, but with limited evidence on long-term effects[11,12,15]. Besides pharmacological interventions, frequently used non-pharmacological treatments, such as acupuncture, exercise programs, cranial electrotherapy stimulation and psychological therapies such as cognitive behavioral therapy are used[15,16]. Little evidence is found on the effectiveness of these treatments on pain relief[15,16].
      It is important to gain a better understanding of SCI-related pain during inpatient rehabilitation in order to improve future treatment. Presence of SCI-related pain tends to change over time, therefore studies on pain in community dwelling patients with SCI might not relate to pain at inpatient rehabilitation[3]. Large studies on the presence of pain during inpatient rehabilitation are scarce and do not report the type of pain[17], or do not relate the patient and lesion characteristics to the type of pain[18]. Finding patient and lesion characteristics associated with SCI-related pain and type of pain, can identify which patients are at risk for developing pain and facilitate patient screening during inpatient rehabilitation. Addressing pain at an early stage could potentially benefit treatment on the long term. The objective of this study is to describe the prevalence of SCI-related pain during inpatient rehabilitation, to describe the characteristics of such pain, and investigate possible associations to different patient and lesion characteristics.

      Methods

      Participants

      This study uses data from the Dutch Spinal Cord Injury Database (DSCID)[19]. The DSCID is a joint effort of the eight SCI specialized Dutch rehabilitation centers. This study used data of the DSCID collected between November 2013 and August 2019. Patients were included in the current study if data on presence of pain (yes or no) was available at both admission and discharge, did not object to the sharing of de-identified data and if time between onset of SCI and admission to the rehabilitation center was within nine months (to exclude readmissions).

      Procedure

      This study was conducted according the principles of the Declaration of Helsinki. Informed consent varies between centers. Some centers ask for written informed consent in advance, where other centers inform patients with oral and written information about the use of anonymous data for research purposes. Patients can decline the use of these data, including the data of the DSCID. Clinical data of patients with SCI were collected upon admission and discharge. A designated member of the clinical staff is responsible for data collection at each center. Information is either retrieved from the electronic medical record retrospectively or added prospectively upon admission of the patient to the rehabilitation center and entered into the DSCID anonymously. The notation in the electronic medical record or the admission to the rehabilitation center is always supervised by a SCI rehabilitation physician. In this way, entering NocP or NeuP is similar in all rehabilitation centers.

      Instruments

      The DSCID contains data on age, sex, etiology of SCI, various secondary conditions of SCI, functional status and quality of life. American Spinal Injury Association Impairments Scale (AIS) classification and neurologic level of injury were assessed according to the International Standards for Neurological Classification of Spinal Cord Injury, revised version of 2011[20]. Data on pain was collected according to an amendment to the Spinal Cord Injury Pain Basic Data Set, which was a shorter version[21]. Information on the presence of pain, the type of pain divided into NocP (which were subdivided into musculoskeletal and visceral pain), NeuP (which was divided into above level, at level and below level of injury, where at level pain extends to 3 levels below the level of injury) and other pain, intensity of pain on the 11-point numeric rating scale (NRS), treatment of pain and type of treatment (oral medication, physiotherapy, psychology and other) was available from the DSCID.

      Analysis

      The statistical analyses were performed using IBM SPSS Version 26 (IBM, Armonk NY). Frequencies were reported on the sociodemographic characteristics of the included patients and the characteristics of pain. Independent samples T-tests were used to compare means for continuous variables and chi-squared tests were used to compare categorical variables on baseline characteristics of patients included and excluded from the DSCID. An independent samples T-test was used to compare mean time since onset between patients with pain and without pain. Logistic regression analyses were performed to examine whether a prediction on the prevalence of pain could be made using the variables age, sex, etiology, AIS-classification and level of injury for which unadjusted and adjusted odds ratios were calculated. Little's MCAR tests were used to evaluate whether missing data was distributed randomly.

      Results

      From a total of 2700 patients registered in the DSCID, 1432 were included in the analysis. A flow diagram of inclusion of patients is shown in figure 1. Patient characteristics at admission of the included and excluded patients are shown in table 1. The included group contained less patients with AIS A and more patients with AIS D compared to the excluded group. Exclusion of patients readmitted to the rehabilitation center (time since onset > 9 months) resulted in a significant difference in time since onset between included and excluded patients. Among the included patients, most common causes of traumatic SCI were falls (54.5%), traffic accidents (22.3%) and sports-related accidents (14.3%). Most common causes of non-traumatic SCI were vascular (22.4%), benign or malignant tumor growth (21.8%), degeneration (20.8%) and inflammation (15.9%). Most patients had an incomplete SCI in which AIS D occurred most frequently.
      Table 1Patient characteristics at admission
      Included participants = 1432Excluded participants = 1268P-value
      n (%)n (%)
      Sex

      Female

      Male



      Missing


      507 (35.4)

      925 (64.6)

      0


      465 (36.7)

      801 (63.3)

      2
      0.474
      Age

      Years. mean ± SD

      Years. median (IQR)

      Missing


      56.8 ± 16.5

      60 (22)

      10


      57.3 ± 16.8

      61 (23)

      6
      0.334
      Time since onset at admission

      Days, mean ± SD

      Days, median (IQR)

      Missing


      38.2 ± 45.9

      22 (26)

      0


      564 ± 2301

      30 (56)

      340
      0.000*
      Length of stay

      Days, mean ± SD

      Days, median (IQR)

      Missing


      92.4 ± 78.7

      70 (84)

      43


      90.38 ± 65

      72 (74.5)

      547
      0.595
      AIS classification

      AIS A

      AIS B

      AIS C

      AIS D

      Missing


      159 (12.3)

      125 (9.7)

      183 (14.2)

      825 (63.9)

      140




      160 (18.4)

      92 (10.6)

      127 (14.6)

      492 (56.5)

      397
      0.000*

      Etiology of SCI

      Traumatic

      Non-traumatic

      Missing


      566 (40.1)



      846 (59.9)

      20




      417 (36.5)

      727 (63.5)

      124
      0.060
      Tetraplegia/paraplegia

      Tetraplegia

      Paraplegia

      Missing


      557 (43.5)

      722 (56.5)

      153


      412 (47.5)

      455 (52.5)

      401
      0.070
      Abbreviations: AIS, American Spinal Injury Association Impairment Scale
      *significant difference between groups
      Prevalence of pain is reported in table 2. Pain was reported in 61.1% at admission and 51.5% at discharge. NocP was reported in 40.4% of the patients at admission and in 26.1% at discharge. NeuP was reported in 30.5% of the patients at admission and 31.7% at discharge. Change in pain is reported in table 3. Characteristics of NocP and NeuP are shown in table 4 and 5 respectively. Above level NeuP was described as other NeuP. This occurred in three patients, of which two had a combination with at level and below level NeuP.
      Table 2Prevalence of pain at admission and discharge
      Total participants = 1432n (%)AdmissionDischarge
      Total pain

      Yes

      No


      877 (61.2)

      555 (38.8)


      737 (51.5)

      695 (48.5)
      Nociceptive pain

      Yes





      No

      Missing


      556 (40.6)





      814 (59.4)



      62


      352 (26.0)

      1002 (74.0)

      78
      Neuropathic pain

      Yes

      No

      Missing


      411 (30.2)

      951 (69.8)

      70


      436 (31.4)

      952 (68.6)

      44
      Other pain

      Yes

      No

      Missing


      74 (5.4)

      1296 (94.6)

      62


      78 (5.7)

      1293 (94.3)

      61
      Table 3Change in pain during inpatient rehabilitation
      N (%)At dischargeYesNo
      Total pain at admission

      Yes

      No


      580 (66.1)

      157 (28.3)


      297 (33.9)

      398 (71.7)
      Nociceptive pain at admission

      Yes

      No



      Missing*


      230 (43.7)

      104 (13.4)

      129




      296 (56.3)

      673 (86.6)

      Neuropathic pain at admission

      Yes

      No

      Missing*


      240 (59.4)

      176 (19.0)



      104


      164 (40.6)

      748 (81.0)

      Other pain at admission

      Yes

      No

      Missing*


      9 (12.9)

      66 (5.3)

      106


      61 (87.1)

      1180 (94.7)
      *Missing data on type of pain at admission and/or discharge
      Table 4Characteristics of nociceptive pain
      Patients with nociceptive pain at admission (n=556)n (%)Patients with nociceptive pain at discharge (n=352)n (%)
      Pain intensity

      NRS, mean ± SD (min-max)

      NRS, median (IQR)

      Missing


      4.37 ± 2.15 (0-10)

      4 (3)

      244


      4.19 ± 2.12 (0-10)

      4 (3)

      102
      Type of pain n (%)

      Musculoskeletal pain

      Visceral pain

      Other

      Missing


      448 (90.7)

      26 (5.3)

      20 (4.0)

      62


      250 (92.3)

      12 (4.4)

      9 (3.3)

      81
      Treatment n (%)

      Yes

      No

      Missing


      486 (93.6)

      33 (6.4)

      37


      291 (85.6)

      49 (14.4)

      12
      Type of treatment n (%)*

      Oral medication

      Physiotherapy

      Psychotherapy

      Other


      475 (91.5)

      77 (14.8)

      1 (0.2)

      13 (2.5)


      270 (79.4)

      96 (28.2)

      4 (1.2)

      16 (4.7)
      Abbreviation: NRS, Numeric Rating Scale; SD, Standard Deviation; IQR Interquartile Range.
      * % of included patients suffering from nociceptive pain and with data on treatment. Multiple treatments or no treatment can be used in one patient. Therefore total percentages can exceed or be lower than 100%.
      Table 5Characteristics of neuropathic pain
      Patients with neuropathic pain at admission (n=411)n (%)Patients with neuropathic pain at discharge (n=436)n (%)
      Pain intensity

      NRS, mean ± SD (min-max)

      NRS, median (IQR)

      Missing


      4.69 ± 2.15 (0-10)

      5 (4)

      156


      4.38 ± 2.29 (0-10)

      4 (3)

      84
      Level of pain n (%)

      At level

      Below level

      At and below level

      Other

      Missing


      82 (22.3)

      214 (58.2)

      65 (17.7)

      7 (1.9)

      43


      85 (21.9)

      223 (57.3)

      70 (18.0)

      11 (2.8)

      47
      Treatment n (%)

      Yes

      No

      Missing


      291 (72.6)

      110 (27.4)

      10


      352 (82.7)

      74 (17.3)

      8
      Type of treatment n (%)*

      Oral medication

      Physiotherapy

      Psychotherapy

      Other


      287 (71.6)

      17 (4.2)

      1 (0.2)

      5 (1.2)


      346 (80.8)

      41 (9.6)

      5 (1.2)

      14 (3.3)
      Abbreviation: NRS, Numeric Rating Scale; AIS, American Spinal Injury Association Impairment Scale
      *% of included patients suffering from nociceptive pain and with data on treatment. Multiple treatments or no treatment can be used in one patient. Therefore total percentages can exceed or be lower than 100%
      Time since onset of SCI was not significantly different in the group with pain and without pain in the total sample (mean 38.1 days and 38.2 days (p = 0.96) at admission and mean 130 and 126 days (p = 0.39) at discharge, respectively), nor in the subgroups with nociceptive pain (44.8 and 47.6 days (p = 0.47) at admission and 126 and 129 days (p = 0.56) at discharge, respectively) and neuropathic pain (38.7 and 37.3 days (p = 0.63) at admission and 132 and 136 days (p = 0.25) at discharge).

      Patient characteristics on pain

      The odds ratios of NocP and NeuP in relationship to patient characteristics is shown in table 6 and 7 respectively. At admission, patients with AIS B compared to AIS D had a lower risk of having NocP. Patients with traumatic SCI had a higher risk of having NocP. At discharge female patients and patients with traumatic SCI had a higher risk of having NocP and patients with AIS C compared to AIS D had a lower risk of having NocP. Sex, age, etiology and level of injury showed significant relations to the prevalence of NeuP. At admission female patients had a higher risk of having NeuP. At discharge female patients, patients aged <65 compared to >75 and tetraplegic patients had a higher risk of having NeuP.
      Table 6Prevalence of Nociceptive pain in relationship to patient and lesion characteristics
      AdmissionDischarge
      Patients with pain (n=556)Patients with pain versus without painPatients with pain (n=352)Patients with pain versus without pain
      n (%)bUnadjusted OR(95% CI)Adjusted ORa(95% CI)n (%)bUnadjusted OR(95% CI)Adjusted ORa(95% CI)
      Sex

      Female

      Male

      Missing


      199 (41.3)

      357 (40.2)

      0


      1.05 (0.84 – 1.31)

      1.00


      1.10 (0.86 – 1.41)

      1.00


      138 (29.2)

      214 (24.3)

      0


      1.28 (1.00 – 1.65)

      1.00


      1.37 (1.04 – 1.82)*

      1.00
      Age

      ≤44

      45-54

      55-64

      65-74

      ≥75

      Missing


      135 (44.7)

      99 (44.4)

      106 (35.2)

      142 (39.4)

      71 (40.8)

      3


      1.17 (0.80 – 1.71)

      1.16 (0.78 – 1.73)

      0.79 (0.54 – 1.16)

      0.95 (0.65 – 1.37)

      1.00


      1.04 (0.68 – 1.59)

      1.07 (0.69 – 1.66)

      0.78 (0.51 – 1.18)

      0.96 (0.65 – 1.44)

      1.00


      78 (25.7)

      60 (27.0)

      81 (27.6)

      89 (24.9)

      41 (24.4)

      3


      1.07 (0.69 – 1.66)

      1.15 (0.72 – 1.82)

      1.18 (0.76 – 1.82)

      1.03 (0.67 – 1.58)

      1.00



      1.05 (0.64 – 1.73)

      1.05 (0.63 – 1.76)

      1.20 (0.74 – 1.96)

      1.05 (0.66 – 1.68)

      1.00
      AIS classification at admission

      AIS A

      AIS B

      AIS C

      AIS D

      Missing


      74 (47.7)

      40 (33.3)

      65 (36.9)

      323 (40.9)

      54


      1.32 (0.94 – 1.87)

      0.72 (0.48 – 1.08)

      0.85 (0.60 – 1.19)

      1.00


      1.02 (0.70 – 1.50)

      0.64 (0.42 – 0.98)*

      0.71 (0.50 – 1.01)

      1.00


      45 (29.2)

      23 (19.3)

      34 (20.2)

      202 (25.8)

      48


      1.19 (0.81 – 1.74)

      0.69 (0.43 – 1.12)

      0.73 (0.49 – 1.10)

      1.00



      1.01 (0.65 – 1.58)

      0.69 (0.42 – 1.14)

      0.60 (0.38 – 0.93)*

      1.00

      Etiology of the SCI

      Traumatic

      Non-traumatic

      Missing


      262 (48.2)

      287 (35.6)

      7


      1.68 (1.35 – 2.10)*

      1.00


      1.98 (1.50 – 2.62)*

      1.00


      157 (29.5)

      191 (23.8)

      4


      1.35 (1.05 – 1.71)*

      1.00


      1.53 (1.12 – 2.09)*



      1.00
      Level of injury

      Tetraplegia

      Paraplegia

      Missing


      220 (40.7)

      279 (40.7)



      57


      1.00 (0.80 – 1.26)

      1.00


      0.83 (0.64 – 1.07)

      1.00


      129 (24.6)

      173 (25.1)

      50


      0.97 (0.75 – 1.26)

      1.00


      0.95 (0.68 – 1.24)

      1.00
      OR = odds ratio, a = adjusted for sex, age, time since onset, AIS classification, etiology of SCI and level of injury; b = percentage of pain within subgroup
      *statistically significant (CI ≠ 1.00); Abbreviation: AIS, American Spinal Injury Association Impairment Scale
      Table 7Prevalence of Neuropathic Pain in relationship to patient and lesion characteristics
      AdmissionDischarge
      Patients with pain (n=411)Patients with pain versus without painPatients with pain (n=436)Patients with pain versus without pain
      n (%)bUnadjusted OR (95% CI)Adjusted ORa (95% CI)n (%)bUnadjusted OR (95% CI)Adjusted ORa (95% CI)
      Sex

      Female

      Male

      Missing


      158 (32.6)

      253 (28.8)

      0


      1.20 (0.94 – 1.52)

      1.00


      1.35 (1.04 – 1.76)*

      1.00


      183 (37.2)

      253 (28.2)

      0


      1.51 (1.19 – 1.90)*

      1.00


      1.69 (1.30 – 2.20)*

      1.00

      Age

      ≤44

      45-54

      55-64

      65-74

      ≥75

      Missing


      103 (34.6)

      82 (35.7)

      84 (28.3)

      96 (27.0)

      43 (25.0)

      3


      1.59 (1.04 – 2.41)*

      1.66 (1.07 – 2.58)*

      1.18 (0.77 – 1.81)

      1.11 (0.73 – 1.68)

      1.00


      1.56 (0.98 – 2.48)

      1.54 (0.96 – 2.47)

      1.07 (0.67 – 1.70)

      0.98 (0.62 – 1.53)

      1.00


      98 (31.7)

      83 (36.6)

      102 (33.8)

      108 (29.4)

      41 (23.7)

      4


      1.50 (0.98 – 2.29)

      1.86 (1.19 – 2.89)*

      1.64 (1.08 – 2.51)*

      1.34 (0.89 – 2.04)

      1.00



      1.89 (1.16 – 3.07)*

      2.23 (1.35 – 3.67)*

      2.08 (1.29 – 3.37)*

      1.55 (0.97 – 2.48)

      1.00
      AIS classification at admission

      AIS A

      AIS B

      AIS C

      AIS D

      Missing


      47 (30.1)

      31 (25.8)

      50 (28.4)

      239 (30.5)

      44


      0.98 (0.68 – 1.43)

      0.79 (0.51 – 1.23)

      0.91 (0.63 – 1.30)

      1.00


      0.82 (0.54 – 1.24)

      0.74 (0.47 – 1.17)

      0.85 (0.58 – 1.24)

      1.00


      54 (34.0)

      38 (30.9)

      53 (30.5)

      243 (30.3)

      48


      1.18 (0.82 – 1.70)

      1.03 (0.68 – 1.55)

      1.01 (0.71 – 1.44)

      1.00





      1.08 (0.71 – 1.65)

      1.02 (0.66 – 1.58)

      0.86 (0.58 – 1.27)

      1.00

      Etiology of the SCI

      Traumatic

      Non-traumatic

      Missing


      176 (32.7)

      229 (28.5)

      6


      1.22 (0.96 – 1.55)

      1.00


      1.31 (0.98 – 1.77)

      1.00


      194 (35.3)

      238 (29.0)

      4
      1.34 (1.06 – 1.69)*

      1.00


      1.31 (0.98 – 1.74)

      1.00
      Level of injury

      Tetraplegia

      Paraplegia

      Missing


      168 (31.1)

      194 (28.5)

      49


      1.13 (0.89 – 1.45)

      1.00


      1.09 (0.83 – 1.44)

      1.00


      185 (34.1)

      201 (28.6)

      50


      1.30 (1.02 – 1.65)*

      1.00


      1.32 (1.00 – 1.74)*

      1.00
      OR = odds ratio, a = adjusted for sex, age, time since onset, AIS classification and etiology of SCI and level of injury; b = percentage of pain within subgroup
      *statistically significant (95% CI ≠ 1.00)
      Abbreviation: AIS, American Spinal Injury Association Impairment Scale.

      Missing data

      Little's MCAR tests showed that missing data was distributed randomly and did not occur more frequently in specific subgroups.

      Discussion

      In our population of 1432 patients with newly acquired SCI, pain is highly prevalent. The prevalence of NocP decreased during inpatient rehabilitation and prevalence of NeuP stayed the same. Female patients and patients having traumatic SCI had a higher risk of having NocP. Female patients, younger patients and tetraplegic patients had a higher risk of having NeuP.
      The prevalence of pain reported in this study, is lower than reported in the current literature. One study performed in Switzerland on pain during inpatient rehabilitation, reported a pain prevalence of 87% at admission and 74% at discharge[17]. This study did not make a distinction between different types of pain. Another study performed in Italy on pain at inpatient rehabilitation showed a prevalence of 72% during inpatient stay with a prevalence of NocP and NeuP of 52% and 48% respectively[18]. Most studies report the presence of pain in community dwelling patients with SCI, which is different from pain prevalence at inpatient rehabilitation. In a recent meta-analysis, with large variation in time since onset, the pooled prevalence of musculoskeletal pain was 56% and the pooled prevalence of visceral pain was 20%[22]. The differences in prevalence between the studies can also be explained by the different patient characteristics of the studies. Musculoskeletal pain could develop in long term wheelchair users (range 5-56 years) due to overuse of the upper extremity, spasticity and muscle contractures[23]. During inpatient rehabilitation there seems to be a decrease in NocP. Table 3 shows that 296 patients cease to have NocP during inpatient rehabilitation, while 104 develop NocP. This could be explained by pain resulting from the trauma or surgery disappearing over time. It is also possible that intensive physical treatment from a physical therapist during inpatient rehabilitation has a positive effect on managing NocP symptoms as has been described for SCI-related shoulder pain in wheelchair users for over 1 year[24]. Increased use of physical therapy as a treatment for NocP during inpatient rehabilitation is also described in table 4, where 28.2% of patients with NocP use physical therapy as a treatment compared to 14.8% at admission. Inactivity during hospitalization could also explain the higher pain levels of NocP at admission and decrease at discharge as training with a physical therapist increases during inpatient rehabilitation. The fact that inpatients start using wheelchairs however, could explain the portion of patients that develop NocP during inpatient rehabilitation, as rotator cuff pathology occurs more frequently in manual wheelchair users with SCI[25].
      The prevalence of NeuP reported in this study is lower than other studies report. A wide range of percentages on the prevalence of NeuP exist in current literature, varying between 32% and 92%[26–33]. Meta-analyses published in 2017 and 2021 estimated the pooled prevalence of NeuP to be 53% and 58% respectively[8,22]. This study collected information during inpatient rehabilitation and therefore did not examine the prevalence of NeuP over a longer period of time. As shown in table 3, the number of patients that develop NeuP during inpatient rehabilitation is similar to the number of patients that cease to have NeuP (176 vs 164 respectively). NeuP mostly develops in a few years’ time and prevalence increases after 1 year[8,26,28]. Most patients reported NeuP to be present below level of lesion. Other studies also report NeuP to be mostly present below neurologic level of injury[28,30–32,34,35]. In the meta-analysis of Burke et al., pooled prevalence of at-level NeuP in patients with SCI was 19% whereas pooled prevalence of below-level NeuP was 27%[8]. In this study, the prevalence of NeuP can only be generalized to patients with SCI during inpatient rehabilitation and not the entire SCI population. Long term follow-up at inpatient rehabilitation and after discharge would be useful to study the change in pain over time.
      Demographic characteristics in this study were comparable to other studies on SCI. Mean age at admission was 57 years. The mean age in other studies on SCI range from 40 to 62 years[3,36–42]. The majority of patients (64.6%) in this study are male, which is similar to other studies[4,37,43]. Etiology of SCI is comparable to many other studies that include both traumatic and non-traumatic SCI[37,42,43]. A minority of the patients in this study had a complete SCI (AIS A). This low number of complete SCI is in accordance to other SCI studies[3,36,37]. There are differences on demographics in different parts of the world, for example traumatic SCI is more prevalent in Northern America compared to Western Europe [44].
      The mean pain intensity of NocP and NeuP reported in this study is comparable to other studies reporting pain during inpatient rehabilitation[17,45]. It is lower compared to other studies reporting on pain in the 5 to 8 years post-injury, where pain ranged from 5.7 to 5.8 on the NRS in musculoskeletal pain, 6.6 in visceral pain and 5.7 to 6.4 in NeuP[3,35]. This difference could be explained by pain worsening over time, as described before[5]. It is likely that assessment in other studies focus solely on pain, which could have led to a higher score on the NRS due to selection bias. Patients included in the current study were assessed on multiple questions regarding their SCI. This could have led to the large amount of missing data on NRS as the priority might not have been on pain during their inpatient rehabilitation.
      A meta-analysis performed on determinants of pain in SCI did not find a relationship between pain and patient or lesion characteristics[4]. In this study females and patients having a traumatic SCI had a higher risk of having NocP and female patients, patients aged <65 and tetraplegic patients had a higher risk of having NeuP. Other studies also found sex to be of influence on SCI-related pain, where pain is related to female sex[26,46,47]. This could also be explained by the different presentation of pain in sex, unrelated to SCI[48]. In accordance with results on this study, Siddall et al. described tetraplegic patients to have a positive correlation to having NeuP[3]. A study in the Swiss population found that chronic pain, with no distinction between types of pain, was more prevalent in the oldest age group (≥61 years) compared to the youngest age group (16-30 years)[46]. Another study at inpatient rehabilitation also found that having pain was related to older age[18]. These studies did not differentiate between types of pain. The relationship between age and specifically having NeuP has not been described in previous research.
      This study found a lower risk for NocP for patients suffering from AIS B and AIS C. There was no relationship between the presence of NeuP and injury severity. Up until now, only few studies have investigated the influence of injury severity on pain, mostly on the presence of NeuP. Different studies show conflicting results on the relationship between injury severity and pain. Norrbrink Budh et al. reported that patients with AIS D had a significantly higher prevalence of SCI-related pain compared to patients with other AIS classifications[47]. In contrast, Werhagen et al. showed patients with complete SCI (AIS A) had more below-level NeuP than patients with incomplete SCI[31]. Another study of Werhagen et al. showed no difference between injury severity and the prevalence of NeuP in non-traumatic SCI[32]. Siddall et al. reported that allodynia was more present in patients with incomplete lesions[49]. A better understanding of the relationship between pain and injury severity can possibly be achieved if the pathophysiology of pain is further explained or a more in depth assessment of pain characteristics is performed.

      Study limitations

      Several limitations of this study deserve to be mentioned. First, this study only reports on pain during initial inpatient rehabilitation. Therefore the prevalence of pain can only be generalized to patients during inpatient rehabilitation, with a short time since onset of SCI. Second, this study describes presence on pain, type of pain, type of treatment and NRS but does not report on further information such as type of medication or burden caused by pain. Third, the DSCID has a high percentage of missing data. Due to the fact that data collection is either done prospectively at admission or by extracting information from the electronic medical record, the amount of missing data could have been caused by a lack of information in the electronical medical record. Also, in most cases there is a delay in entering data in the DSCID making it difficult to retrieve missing data from the patient. Future funding could possibly create time in which data is collected routinely prospectively in the different centers. This could enhance data completeness and accuracy as has been described before[19]. Last, there is a significant difference in AIS classifications in the included and excluded group. Patients with complete SCI were less likely to have data on presence of pain at both admission and discharge. This could be explained by the fact that patients with complete SCI are admitted longer to the rehabilitation center and the information at discharge is not yet collected. In addition, there are more patients with AIS D in the analysis, which could have led to an overestimation of the prevalence of NocP, as participants with AIS D were more likely to have NocP compared to AIS B and C.

      Conclusions

      This study showed that SCI-related pain is highly prevalent during initial inpatient rehabilitation. Prevalence of NocP decreased during inpatient rehabilitation and prevalence of NeuP remained the same. Pain intensity was similar for different types of SCI-related pain with a score on the 11-point NRS with means ranging from 4.19 (NocP at discharge) to 4.69 (NeuP at admission) . Female patients and patients with traumatic SCI have a higher risk of having NocP and female patients, patients aged <65 and tetraplegic patients have a higher risk of having NeuP. Patients with AIS B and C compared to AIS D have a lower risk of having NocP. These differences in pain prevalence between different groups of patients with SCI are important in screening patients on having pain and developing pain during inpatient rehabilitation.

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