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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

Objective

To determine the clinical usefulness of spinal mobility measurements used for ankylosing spondylitis (AS) to assess spinal involvement in patients with psoriatic arthritis (PsA).

Methods

We assessed 100 patients with PsA and 103 patients with AS. Patients were classified as having axial PsA if they had grade 2 or higher unilateral sacroiliitis in the presence of spinal symptoms. All PsA patients, without taking the degree of joint involvement into consideration, were evaluated using several measurements for AS. Spinal measurements were compared with axial and peripheral forms of PsA, and the ability of the techniques to discriminate between the 2 forms of PsA was analyzed using the Mann-Whitney U test and the area under the receiver operating characteristic (ROC) curve. A logistic regression model was used to determine the best measurements for evaluating axial PsA. Finally, the results of measurements for axial PsA were compared with those for AS.

Results

Of the 100 PsA patients, 46 met the classification criteria for axial PsA, which presented more severe spinal measurement assessments compared with peripheral PsA. Modified Schober test, lumbar side flexion, chest expansion, and cervical rotation measurements performed best under the ROC curve. Modified Schober test, lumbar side flexion, and cervical rotation were the more suitable measurements for assessing axial PsA. There were only minor differences between axial PsA and AS.

Conclusion

The spinal measurements used to evaluate AS performed well to assess spinal involvement in PsA. These measurements, notably the modified Schober test, lumbar side flexion, and cervical rotation, should be used in daily clinical practice to assess PsA patients with spinal involvement.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

The classification criteria for psoriatic arthritis (CASPAR) were developed by the Group for Research and Assessment in Psoriasis and Psoriatic Arthritis with the aim of improving current issues with the definition and classification of psoriatic arthritis (PsA) (1). According to CASPAR criteria, inflammatory articular disease in PsA should be considered if the joint, the spine, or enthesis are involved; however, no accurate definition of these concepts has been developed.

Classically, clinical joint involvement in PsA has been divided into 5 subgroups. Although this clinical classification has been challenged and remains controversial (2), it seems certain that spinal involvement in clinically diagnosed PsA (axial PsA) has a prevalence between 40% and 78% (3, 4), depending on the criteria utilized for classification.

Although the assessments and outcomes of peripheral joint involvement in PsA are somewhat similar to those of rheumatoid arthritis (5, 6), accurate methods for evaluation of axial PsA have not been established. One reason for this is the absence of a good definition for axial PsA. Axial PsA can be defined based on 2 aspects: either clinical or radiologic evaluations. Clinically, axial PsA would be defined as a combination of inflammatory spinal symptoms and limitation of movement, whereas radiologically, axial PsA would be defined using only radiologic criteria. A combination of clinical and radiologic features would seem to be a more appropriate way for making this classification. However, as of yet there is no consensus on the best approach to achieve definitive classification (7, 8).

For assessment purposes, axial PsA could be considered similar to ankylosing spondylitis (AS) (9, 10). Recent work has demonstrated that measuring spinal mobility, particularly using cervical rotation, chest expansion, the modified Schober test, and lateral bending of the spine as used in assessing primary AS, is reliable and reproducible when applied to axial PsA (11). However, because of the small number of cases included in that study, a larger number of cases from clinical practice needs to be evaluated.

Several reasons underlie the need for an accurate clinical evaluation of axial PsA (12). In clinical practice, there is currently no established way for classifying and evaluating spinal involvement in PsA. Therefore, spinal disease may not be properly recognized and the incidence of spinal involvement in PsA patients may be underestimated. Because spinal evaluations are not performed regularly in axial PsA, we cannot evaluate the outcome or the efficacy of the treatments used for spinal involvement; this issue is particularly important in this era of biologic treatments. Finally, the lack of clear-cut techniques for evaluating axial PsA provides no criteria for initiation of conventional or biologic therapy.

The objectives of this study were to 1) evaluate the utility of primary AS spinal mobility measurements in the assessment of spinal involvement in PsA, 2) analyze which of these measurements provides the best evaluation of axial PsA, and 3) compare the clinical data and spinal mobility measurements of axial PsA with those of primary AS.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

Study design and population.

The first 100 patients diagnosed with PsA at a PsA clinic, established in January 2007 at the Hospital Universitario Juan Canalejo in La Coruña, Spain, were studied. The patients were diagnosed using the Moll and Wright criteria (however, all patients also met the present CASPAR criteria) and all patients were negative for rheumatoid factor (13).

All patients were evaluated and assessed regardless of clinical presentation. The clinical data collected included morning stiffness, swollen joint count (n = 76), tender joint count (n = 78), patient assessment of pain on a visual analog scale (VAS), patient global assessment of disease activity (VAS), physician global assessment of disease activity (VAS), and Health Assessment Questionnaire (HAQ) responses. For all patients, axial involvement was evaluated using the following measurements: occiput-to-wall distance, chest expansion, modified Schober test, lateral lumbar flexion, intermalleolar distance, and cervical rotation. Cervical rotation was measured with a plastic baseline 360° ISOM goniometer (Next Gen Ergonomics, Quebec, Canada) and was scored as: 0 = >70°, 1 = 20–70°, and 2 = <20°. These measurements were performed according to standard publishing techniques (11, 14–16). Enthesitis was evaluated, because of its feasibility, using the Maastricht Ankylosing Spondylitis Enthesitis Score (17). Back pain caused by PsA during the past week was assessed using a VAS score for both nocturnal pain and overall pain. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (18), the Bath Ankylosing Spondylitis Functional Index (BASFI) (19), and the Short Form 12 Health Survey (20) scores were also recorded. The erythrocyte sedimentation rate (mm/hour) and C-reactive protein level (mg/dl) were also collected.

As the control group for this study, 103 patients meeting the modified New York criteria for the classification of AS who were followed at the AS clinic during the year 2006 were used (21). These patients were evaluated by collecting the same clinical data and making the same measurements utilized for PsA, except for morning stiffness and the patient assessment of pain on VAS and the HAQ. The same physician (JLF-S) collected the clinical data and performed the physical examinations of both cohorts.

The entire spine of every patient was examined by radiograph and read following the Bath Ankylosing Spondylitis Radiology Index (BASRI) radiologic scoring method (22). Reading and scoring of radiographs was performed by consensus of 2 members of our group (AW and JAPT).

For this study, patients were classified as having axial disease if they had at least grade 2 unilateral sacroiliitis in the presence of spinal symptoms (defined as a combination of inflammatory back pain plus back stiffness). The PsA patients were classified as pure axial if they had no peripheral joint involvement, mixed if they had both peripheral joint arthritis and axial disease, or as peripheral joint involvement alone. Those patients who met the classification of axial disease independent of peripheral joint involvement were used for this study.

This study was performed with approval from the ethics committee of the institution, and informed consent was obtained from all patients.

Statistical analyses.

A descriptive analysis of the variables studied was performed, comparing patients with axial PsA with patients with peripheral PsA and AS. The analyses were performed separately for PsA patients with pure axial and mixed disease. For univariate analyses, the comparison of quantitative variables was done using the Mann-Whitney U test. The comparison of qualitative variables was performed using chi-square or Fisher's exact tests. Epidemiologic characteristics, clinical features, spinal and radiologic measures, functional outcomes, and clinical activity levels were compared between axial PsA and AS patients using linear or logistic regression analyses after adjusting for age, sex, and disease duration. We adjusted for these variables because we considered that these variables could have an influence when comparing axial PsA versus AS. Variables that were not normally distributed were log-transformed or squared before linear regression analysis.

The performance of the different spinal measurement techniques for discriminating between axial PsA and peripheral PsA was evaluated utilizing receiver operating characteristic curves, the area under the curve (AUC), and its 95% confidence interval (95% CI). A multiple logistic regression model was used to determine the techniques that were best for the clinical assessment of axial PsA. All measurements except cervical rotation were included in the logistic regression model as quantitative variables.

Correlations between spinal measurements and the degree of radiologic sacroiliitis and the BASRI were determined using Spearman's rank correlation coefficient. Correlations between the BASFI and BASRI were also analyzed by this technique.

All hypotheses were 2-tailed and P values less than 0.05 were considered significant. The analyses were performed using SPSS, version 15.0 for Windows (SPSS, Chicago, IL).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

Patients.

A total of 100 PsA patients and 103 AS patients were evaluated. The PsA cohort was composed of 36 women and 64 men, with a mean ± SD age of 55.1 ± 13 years (range 22–78). The AS cohort was composed of 18 women and 85 men, with a mean ± SD age of 48 ± 13.7 years (range 18–77). The mean ± SD disease duration was 12.2 ± 7.9 years (range 1.5–46) for PsA patients and 21.5 ± 13.4 years (range 2–55) for AS patients.

When the PsA patients were classified according to clinical and radiologic data, 46 patients met the criteria for axial PsA disease; 4 had pure axial PsA and 42 had mixed PsA. The remaining 54 patients had peripheral joint disease.

Clinical characteristics.

We present the data from the analysis comparing the 46 patients with axial PsA with the 54 patients with peripheral PsA. Analogous results were obtained from analyses of pure axial PsA and mixed PsA patients compared with those of peripheral PsA patients.

Table 1 shows the epidemiologic, clinical, spinal, and radiologic features for axial PsA and peripheral PsA patients. Men were more prevalent in axial PsA than in peripheral PsA (78.3% versus 51.9%; P = 0.006). The disease duration was longer in axial PsA (mean 14.0 versus 10.7 years; P = 0.048). There were no significant differences between the groups in the type of cutaneous psoriasis or family history of psoriasis.

Table 1. Comparison between epidemiologic, clinical, spinal, and radiologic features of patients with axial psoriatic arthritis (PsA) and peripheral PsA*
 Axial and mixed PsA (n = 46)Peripheral PsA (n = 54)P
  • *

    Values are the mean ± SD (median) unless otherwise indicated. VAS = visual analog scale; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASRI = Bath Ankylosing Spondylitis Radiology Index; BASFI = Bath Ankylosing Spondylitis Functional Index; HAQ = Health Assessment Questionnaire.

Age at diagnosis, years45.7 ± 13.6 (46.0)45.7 ± 13.1 (45.5)0.913
Age, years57.0 ± 12.8 (56.5)53.5 ± 13.1 (56.5)0.261
Time of followup, years10.8 ± 6.6 (11.0)8.0 ± 5.8 (7.0)0.029
Disease duration, years14.0 ± 8.4 (13.5)10.7 ± 7.2 (9.0)0.048
Men, no. (%)36 (78.3)28 (51.9)0.006
Family history of psoriasis, no. (%)18 (41.9)27 (50.0)0.425
Type of psoriasis, no. (%)  0.615
 Type I32 (69.6)35 (64.8) 
 Type II14 (30.4)19 (35.2) 
Age at diagnosis, no. (%)  0.257
 <60 years37 (88.1)38 (79.2) 
 ≥60 years5 (11.9)10 (20.8) 
Tender joint count4.0 ± 6.9 (0.0)4.0 ± 6.6 (1.5)0.711
Swollen joint count1.3 ± 3.6 (0.0)1.4 ± 3.9 (0.0)0.627
Morning stiffness, minutes15.0 ± 27.0 (2.5)16.5 ± 32.5 (0.0)0.468
Patient global assessment VAS, cm3.9 ± 2.6 (4.5)3.4 ± 2.7 (3.5)0.362
Physician global assessment VAS, cm2.4 ± 1.9 (2.5)2.4 ± 6.2 (2.0)0.045
Patient assessment of pain VAS, cm4.2 ± 2.8 (5.0)3.6 ± 2.5 (4.0)0.269
Enthesitis, no. (%)23 (50.0)20 (37.0)0.192
Occiput-to-wall distance, cm1.5 ± 3.5 (0.0)0.1 ± 0.1 (0.0)0.003
Chest expansion, cm2.7 ± 1.4 (3.0)3.7 ± 1.3 (3.5)0.001
Modified Schober test, cm2.7 ± 1.4 (3.0)4.1 ± 1.0 (4.0)< 0.001
Lumbar side flexion, cm12.6 ± 7.7 (12.0)16.8 ± 6.7 (17.0)< 0.001
Intermalleolar distance, cm86.7 ± 18.8 (89.5)96.5 ± 11.5 (96.5)0.014
Cervical rotation, no. (%)  < 0.001
 <20°4 (9.1)0 (0.0) 
 20–70°20 (45.5)4 (8.3) 
 >70°20 (45.5)44 (91.7) 
Nocturnal spinal pain past week VAS, cm2.4 ± 3.1 (0.0)1.2 ± 2.3 (0.0)0.062
Overall spinal pain past week VAS, cm2.3 ± 2.9 (0.0)1.0 ± 2.0 (0.0)0.021
BASDAI, cm2.7 ± 1.9 (2.7)1.7 ± 1.8 (1.2)0.010
BASDAI without item 2, cm2.3 ± 1.8 (2.5)1.7 ± 1.8 (1.2)0.056
BASDAI without item 3, cm2.8 ± 2.1 (2.9)1.6 ± 2.0 (1.0)0.005
BASRI spine score, cm5.6 ± 3.1 (4.5)0.3 ± 0.9 (0.0)< 0.001
BASRI total score, cm5.8 ± 3.3 (4.5)0.4 ± 0.9 (0.0)< 0.001
BASFI, cm2.8 ± 2.2 (2.1)1.0 ± 1.4 (0.1)< 0.001
HAQ responses0.4 ± 0.4 (0.4)0.4 ± 0.5 (0.2)0.365

No significant differences in tender joint count, swollen joint count, morning stiffness, and total patient VAS pain rating were found between patients with axial PsA and peripheral PsA. Patients with axial PsA showed significantly higher past week spinal pain scores (mean 2.3 cm versus 1.0 cm; P = 0.021) than patients with peripheral PsA.

AS spinal mobility measurements for the evaluation of spinal involvement in axial PsA.

Analyzing the spinal mobility measurements utilized for the evaluation of AS, we found that patients with axial PsA showed significantly higher occiput-to-wall distance than patients with peripheral PsA (mean 1.5 cm versus 0.1 cm; P = 0.003) (Table 1). Axial PsA patients also had significantly lower chest expansion (mean 2.7 cm versus 3.7 cm; P = 0.001), modified Schober test (mean 2.7 cm versus 4.1 cm; P < 0.001), lumbar side flexion (mean 12.6 cm versus 16.8 cm; P < 0.001), and intermalleolar distance (mean 86.7 cm versus 96.5 cm; P = 0.014) than patients with peripheral PsA (Table 1). The number of patients whose cervical rotation was <70° was higher in axial PsA than in peripheral PsA (54.6% versus 8.3%; P < 0.001) (Table 1).

The measurements that best differentiated axial PsA from peripheral PsA patients were the modified Schober test (AUC = 0.783), lumbar side flexion (AUC = 0.764), and chest expansion (AUC = 0.703) (Table 2). After adjustment, using the logistic regression model, the modified Schober test (odds ratio [OR] 0.446, 95% CI 0.260–0.764), lumbar side flexion (OR 0.912, 95% CI 0.842–0.989), and cervical rotation <70° (OR 5.87, 95% CI 1.518–22.673) were the measurements independently associated with axial PsA.

Table 2. Comparison of the performance of different spinal measurements for evaluating axial psoriatic arthritis (PsA) and peripheral PsA*
 AUCSE95% CI
  • *

    AUC = area under the receiver operating characteristic curve; 95% CI = 95% confidence interval.

Occiput-to-wall distance, cm0.5940.0590.477–0.711
Chest expansion, cm0.7030.0530.599–0.808
Modified Schober test, cm0.7830.0470.690–0.875
Lumbar side flexion, cm0.7640.0500.666–0.863
Intermalleolar distance, cm0.6470.0570.534–0.759
Cervical rotation <70°, %   
 Sensitivity54.5 38.7–70.4
 Specificity91.7 82.8–100
 Positive predictive value85.7 71.0–100
 Negative predictive value68.8 56.6–80.9

Correlation of spinal measurements with radiologic measurements.

Radiographs measured by the BASRI showed higher scores for patients with axial PsA than for those with peripheral PsA (mean BASRI spine score 5.6 versus 0.3 cm; P < 0.001 and mean BASRI total score 5.8 versus 0.4 cm; P < 0.001) (Table 1). All the spinal measurements except intermalleolar distance correlated well with the sacroiliitis grade, BASRI spine score, and BASRI total score. Higher sacroiliitis grades and BASRI scores corresponded with higher occiput-to-wall distance, lower chest expansion, modified Schober test, and lumbar side flexion scores. Higher sacroiliitis grades and BASRI scores were also observed in patients with cervical rotation <70° than in patients with certical rotation >70° (Table 3).

Table 3. Correlation between Bath Ankylosing Spondylitis Radiology Index (BASRI) scores, radiologic sacroiliitis, and spinal measures in 46 patients with axial psoriatic arthritis*
 BASRI spineBASRI totalGrade of radiologic sacroiliitis
  • *

    Values are the Spearman's rank correlation coefficient unless otherwise indicated. IQR = interquartile range.

  • Significant at P < 0.05.

Occiput-to-wall distance, cm0.4560.4510.427
Chest expansion, cm−0.387−0.392−0.373
Modified Schober test, cm−0.559−0.565−0.566
Lumbar side flexion, cm−0.391−0.376−0.421
Intermalleolar distance, cm−0.194−0.192−0.168
Cervical rotation, median (IQR)   
 <70°7 (3–9.25)7 (3–10.25)3 (2–4)
 >70°0 (0–2)†0 (0–2)0 (0–2)†

Measures of functional outcomes.

Physical function as measured by BASFI scores was worse in patients with axial PsA (mean 2.8 cm versus 1.0 cm; P < 0.001) (Table 1). Higher BASFI scores were associated with higher BASRI spine score (rs = 0.377, P < 0.001) and BASRI total score (rs = 0.373, P < 0.001). There were no significant differences in HAQ scores between axial and peripheral forms of PsA.

Clinical activity and treatment.

Clinical activity showed a significant difference between the 2 groups of PsA patients for total BASDAI scores (mean 2.7 cm versus 1.7 cm; P = 0.010) and BASDAI scores without item 3 (pain and swelling in other joints: mean 2.8 cm versus 1.6 cm; P = 0.005) (Table 1). Individual analysis of each item of the BASDAI score found significant differences between axial PsA and peripheral PsA in items 2 (neck, back, or hip pain: mean 3.9 cm versus 1.7 cm; P = 0.001), 5 (level of morning stiffness: mean 2.7 cm versus 1.7 cm; P = 0.25), and 6 (duration of morning stiffness: mean 2.1 cm versus 1.4 cm; P = 0.032) (Table 4). There were no significant differences between axial and peripheral PsA patients attributable to treatment.

Table 4. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) item scores in axial/mixed and peripheral psoriatic arthritis (PsA)*
 Axial or mixed PsA (n = 46)Peripheral PsA (n = 54)P
  • *

    Values are the mean ± SD (median).

Fatigue/tiredness2.5 ± 3.1 (0.0)1.8 ± 2.6 (0.0)0.283
Neck, back, or hip pain3.9 ± 3.3 (5.0)1.7 ± 2.9 (0.0)0.001
Pain and swelling in other joints2.3 ± 3.3 (0.0)2.0 ± 2.7 (0.0)0.771
Discomfort from areas tender to touch2.3 ± 3.2 (0.0)1.3 ± 2.5 (0.0)0.069
Level of morning stiffness2.7 ± 3.2 (1.0)1.7 ± 2.9 (0.0)0.025
Duration of morning stiffness2.1 ± 2.7 (1.0)1.4 ± 2.6 (0.0)0.032

Comparison of axial PsA patients and AS patients.

Comparing the 46 axial PsA patients with the 103 primary AS patients, we found that the axial PsA group was significantly older (mean ± SD age 57.0 ± 12.8 years versus 48 ± 13.7 years; P = 0.001) and their disease duration was statistically shorter (mean ± SD 14.0 ± 8.4 years versus 21.5 ± 8.8 years; P = 0.04). The sex distribution was similar, with 78.3% of the axial PsA patients being men compared with 82.5% in primary AS patients (P = 0.538). The clinical form of the diseases differed, however, in that 8.7% of the axial PsA patients were classified as pure axial compared with 70.9% of primary AS patients (P < 0.001), and 91.3% of axial PsA patients had the mixed form compared with 29.1% of the primary AS patients.

After adjusting for age, sex, and years of disease duration, there were significant differences between axial PsA and AS patients in tender joint count (P < 0.001), nocturnal spinal pain VAS scores for the past week (P = 0.042), overall spinal pain past week VAS scores (P = 0.031), and structural damage measured by BASRI spine (P = 0.015) and BASRI total scores (P = 0.004) (Table 5).

Table 5. Comparison of the clinical features of patients with axial psoriatic arthritis (PsA) and primary ankylosing spondylitis (AS)*
 Axial PsA (n = 46)Primary AS (n = 103)PP
  • *

    Values are the mean ± SD (median). VAS = visual analog scale; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; SF-12 = Short Form 12 Health Survey; BASRI = Bath Ankylosing Spondylitis Radiology Index.

  • Univariate analysis.

  • Adjusted for age, sex, and years of disease duration.

Tender joint count4.0 ± 6.9 (0.0)0.1 ± 0.3 (0.0)< 0.001< 0.001
Swollen joint count1.3 ± 3.6 (0.0)0.0 ± 0.2 (0.0)< 0.001< 0.001
Patient global assessment VAS, cm3.9 ± 2.6 (4.5)3.7 ± 2.6 (3.0)0.5600.591
Physician global assessment VAS, cm2.4 ± 1.9 (2.5)2.6 ± 2.2 (2.0)0.8840.310
Nocturnal spinal pain past week VAS, cm2.4 ± 3.1 (0.0)2.8 ± 2.8 (2.0)0.2490.042
Overall spinal pain past week VAS, cm2.3 ± 2.9 (0.0)2.9 ± 2.8 (2.0)0.1570.031
BASDAI, cm2.7 ± 1.9 (2.6)2.8 ± 1.9 (2.5)0.8090.293
BASFI, cm2.8 ± 2.2 (2.1)3.3 ± 2.6 (2.8)0.4260.838
SF-12 physical component40.1 ± 9.9 (40.6)39.4 ± 10.1 (40.9)0.7730.949
SF-12 mental component46.9 ± 13.5 (53.1)50.5 ± 12.1 (55.9)0.0310.168
BASRI spine score, cm5.6 ± 3.1 (4.5)7.1 ± 3.4 (7.0)0.0080.015
BASRI total score, cm5.8 ± 3.3 (5.8)8.1 ± 4.3 (8.0)0.0020.004

When comparing spinal mobility measurements for axial PsA and AS adjusted for age, sex, and years of disease duration, significant differences were found in the occiput-to-wall distance (mean 1.5 cm versus 4.7 cm; P = 0.003), chest expansion (mean 2.7 cm versus 2.5 cm; P = 0.036), and modified Schober test (mean 2.7 cm versus 1.9 cm; P = 0.027) (Table 6).

Table 6. Comparison of spinal measurements between patients with axial psoriatic arthritis (PsA) and primary ankylosing spondylitis (AS)*
 Axial PsA (n = 46)Primary AS (n = 103)PP
  • *

    Values are the mean ± SD (median) unless otherwise indicated.

  • Univariate analysis.

  • Adjusted for age, sex, and years of disease duration.

Occiput-to-wall distance, cm1.5 ± 3.5 (0.0)4.7 ± 6.3 (0.0)0.0020.003
Chest expansion, cm2.7 ± 1.4 (3.0)2.5 ± 1.9 (2.0)0.3290.036
Modified Schober test, cm2.7 ± 1.4 (3.0)1.9 ± 1.6 (2.0)0.0020.027
Lumbar side flexion, cm12.6 ± 7.7 (12.0)11.3 ± 6.5 (11.5)0.6660.069
Intermalleolar distance, cm86.6 ± 18.8 (89.5)87.9 ± 24.2 (92.0)0.3680.846
Cervical rotation, no. (%)  0.7000.680
 >70°20 (45.5)42 (42.0)  
 <70°24 (54.5)58 (58.0)  

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

The clinical treatment and evaluation of PsA is challenging because of the particular way the disease affects the joints. The affected joint pattern at presentation may change during disease progression, and axial involvement in PsA occurs fairly frequently. Depending on the definition used for classifying axial disease in PsA, 40% to 78% of the patients have spinal involvement. In spite of this high incidence of spinal involvement, there is no consensus on how to classify and evaluate the disease when the spine is involved (23).

Recent clinical trials evaluating newer therapeutic agents have been performed on patients with peripheral arthritis (24). However, although it is believed that these therapeutics work as well in spinal involvement with PsA, there is no hard evidence for this and no established method for evaluating their efficacy in axial PsA.

Some researchers have noted that outcome measures for axial PsA are those used for AS (25); however, the assumption of presumed equivalency may be false. Recent work from the International Spondylarthritis Interobserver Reliability Exercise (INSPIRE) study has shown that several measurements for spinal mobility such as cervical rotation, chest expansion, modified Schober test, and lateral bending of the spine are reliable for assessing AS, and that these measures performed well with respect to interobserver reliability when applied to axial PsA patients (11). In the INSPIRE study, 10 PsA patients with spinal disease were classified on the basis of radiologic evidence of sacroiliitis (at least grade 2) or spondylitis. In our study, we classified patients according to clinical spinal symptoms (inflammatory back pain plus back stiffness) combined with grade 2 or higher unilateral sacroiliitis. Using these criteria for axial disease, it could be argued that some patients having spinal disease may not be properly classified. In psoriatic spinal disease there is poor concordance between radiographic spondylitis and sacroiliitis (26). However, in our study, patients classified as having peripheral PsA have a BASRI spine score of 0.3 (Table 1), whereas patients with a grade 2 unilateral sacroiliitis have both spinal symptoms and a BASRI spine score of 3.1. This higher score is probably because of either lumbar or cervical involvement, but not sacroiliitis alone. Therefore, in our study, all patients classified as having axial PsA also have spondylitis regardless of sacroiliac involvement.

Primary AS measurements in patients classified as having axial PsA showed significant differences from those of PsA patients without spinal involvement. Assessing the performance of several spinal measurements in axial PsA patients, the modified Schober test, lumbar side flexion, chest expansion, and cervical rotation proved to be the most effective for the evaluation of spinal involvement in axial PsA. These results agree with the INSPIRE study for evaluation of spinal measurements in PsA, although in our study the modified Schober test, cervical rotation, and lumbar side flexion measurements demonstrated independent correlations with spinal involvement.

Although there is currently no consensus on how to classify axial PsA and no good correlation between clinical symptoms and radiologic evidence of sacroiliitis and spondylitis (26), in this study we found a strong correlation between the degree of radiologic sacroiliitis and the spinal measurements, similar to recently published results from a smaller study (27). This would suggest that from the time a unilateral grade 2 or higher sacroiliitis appears in the patient, whether or not the patient can be classified as having axial disease, clinical evaluation of the spine should be performed. These results also indicate the need to include radiographs of the sacroiliac when clinically evaluating PsA patients. The BASRI, which measures structural damage in AS, has not yet been validated for PsA, but had the same correlations with spinal measurements as radiologic sacroiliitis.

When we compared axial PsA measurements with those from primary AS patients, we found differences in the degree of spinal pain and in some of the spinal measurements; the important difference concerned peripheral involvement in axial PsA. This is not surprising, because spinal disease in PsA does not necessarily behave as it does in AS. In fact, in this study, only 4% of the patients were classified as having pure axial disease with no accompanying peripheral arthritis.

PsA patients with spinal involvement showed higher BASFI scores compared with those with only peripheral forms, and the BASFI showed good correlation with structural damage measured by the BASRI. This suggests that the BASFI may be a useful tool for measuring function in PsA cases with spinal involvement (19). The HAQ is a good measure for peripheral arthritis, but it did not differentiate between the peripheral and spinal involvement groups and does not seem to be an effective tool for evaluating function when the spine is involved. In this study, the BASDAI also showed differences between axial PsA and peripheral PsA (18). However, the best results were found when item 3, concerning only peripheral arthritis, was not used. These results are quite similar to a previous work that evaluated the BASDAI as a measurement of disease activity in PsA (28). BASDAI scores were also similar in axial PsA compared with primary AS patients, which suggests that the BASDAI may be a useful clinical tool for evaluating spinal inflammation in patients with axial PsA.

In summary, our results confirmed the data from the INSPIRE study in that the spinal measurements used to evaluate primary AS seem suitable to evaluate spinal involvement in PsA, and that these measurements discriminate between peripheral PsA and PsA with spinal involvement. Although no consensus currently exists on how to classify axial PsA, our finding of a correlation between radiologic sacroiliitis and spinal measurements suggest that a patient showing spinal symptoms and radiologic grade 2 or higher sacroiliitis should be evaluated using the modified Schober test, lateral spinal flexion, and cervical rotation measurements. Another important point is that when dealing with spinal involvement in PsA, unlike AS, peripheral involvement will almost always be present.

The BASDAI scores in this study were significantly higher in axial PsA patients compared with peripheral PsA patients and were similar to those of primary AS patients. Therefore, we believe that BASDAI scores should be used as a measure of activity levels in patients with axial PsA.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

Dr. Fernández-Sueiro had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study design. Fernández-Sueiro.

Acquisition of data. Fernández-Sueiro, Willisch, Tasende, Fernández-Lopez, Galdo.

Analysis and interpretation of data. Fernández-Sueiro, Willisch, Pértega-Diaz.

Manuscript preparation. Fernández-Sueiro, Blanco.

Statistical analysis. Pértega-Diaz.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES

We would like to thank Dr. Dafna Gladman for her opinions and the critical review of the manuscript.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
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