Diagnosis & Assessment of Psoriatic Arthritis (PsA)
Psoriatic arthritis Diagnosis of psoriatic arthritis Assessment of psoriatic arthritis Assessment of peripheral arthritis Skin assessment Nail assessment Axial spine assessment Dactylitis assessment Enthesitis assessment Global assessment Laboratory measures Psoriatic arthritis PsA is a chronic inflammatory arthritis that is associated with the skin disease psoriasis. [2] Psoriasis affects 1 - 3%
Diagnosis of psoriatic arthritis
Assessment of psoriatic arthritis
Assessment of peripheral arthritis
Psoriatic arthritis
PsA is a chronic inflammatory arthritis that is associated with the skin disease psoriasis.[2] Psoriasis affects 1 - 3% of the general population, and approximately one-third of patients with psoriasis develop PsA.[3-5] Nail disease, severe skin disease, obesity and a positive family history seem to be the key risk factors for the development of PsA among psoriasis patients.[6] Both psoriasis and PsA significantly negatively impact the patient’s health-related quality of life (HRQoL). Disease-modifying antirheumatic drugs (DMARDs) to treat these diseases have improved outcomes dramatically in recent years.
Diagnosis of psoriatic arthritis
The diagnosis of PsA is made by a combination of clinical findings supplemented by special investigations. The ClASsification for Psoriatic ARthritis (CASPAR) is a useful reference (Table 1).[7]
| Table 1. CASPAR criteria: Confirmed inflammatory articular disease (joint, spine, or entheseal) with ≥3 points is classified as having definite PsA | ||
| Criterion | Details | Points |
| Skin psoriasis (maximum 2 points) | Present | 2 |
| or previously present | 1 | |
| or family history of psoriasis (first- or second-degree relative) | 1 | |
| Nail dystrophy | Oncolysis, pitting, hyperkeratosis | 1 |
| Dactylitis | Current or documented by rheumatologist in past | 1 |
| X-ray hands or feet | Juxta-articular new bone formation | 1 |
| Rheumatoid factor | Negative | 1 |
| CASPAR = ClASsification for Psoriatic Arthritis; PsA = psoriatic arthritis | ||
Assessment of psoriatic arthritis
PsA is a heterogeneous disease, and the group for research and assessment of psoriasis and PsA (GRAPPA) recommends that PsA be assessed in the following five domains: peripheral arthritis; skin and nail disease; axial arthritis; enthesitis; and dactylitis.[8]
Assessment of peripheral arthritis
Compared with rheumatoid arthritis (RA), peripheral joint involvement in PsA is much more extensive. The 28 tender joint count (TJC) and swollen joint count (SJC) used in RA do not represent all the joints affected in PsA. It is recommended that the 68 TJC and 66 SJC are used in PsA.[9,10] The South African Rheumatism and Arthritis Association recommends the Disease Activity in PsA (DAPSA) as a disease activity index for peripheral PsA (Table 2). Based on specific cut-off points, disease activity can be classified into states of remission, low, moderate, or high disease activity.
Skin assessment
In ~70% of patients, psoriasis will antedate the development of the musculoskeletal manifestations. In 10 - 15% of patients, there will be a simultaneous appearance in both skin and musculoskeletal manifestations, and in 10 - 15%, arthritis occurs before psoriasis.[11] In the last group of patients, there may be markers of PsA that may be pointers to the disease, e.g. enthesitis or dactylitis. The two commonly used outcome measures of skin involvement in psoriasis and PsA are the Psoriasis Area and Severity Index (PASI) and body surface area.[12]
Nail assessment
Nail involvement occurs in ~50% of patients with psoriasis, and as many as 80% of patients with PsA.[13-15] A modified Nail Psoriasis Severity Index (mNAPSI) can be used to score nail severity.[16,17]
Axial spine assessment
Axial involvement occurs in ~40% of patients with PsA.[18-20] Although there are similarities between axial SpA (axSpA) (also known as ankylosing spondylitis) and axial involvement in PsA, significant differences are present.[18] The assessment tools and outcome measures for axial involvement in PsA are borrowed from axSpA, including the ankylosing spondylitis disease activity score (ASDAS) or Bath ankylosing spondylitis disease activity index (BASDAI).[21]
Dactylitis assessment
Dactylitis is a term used to describe swelling of the entire digit, and is defined as a >10% difference in the circumference base of the digit compared with the normal contralateral digit.[21] Dactylitis occurs in ~40% of patients with PsA. A simple numerical count of the fingers involved is used in the Leeds Dactylitis Index.
Enthesitis assessment
Enthesitis is prevalent in 25 - 78% of patients with PsA, and may sometimes be the presenting feature.[22] It is thought that the “deep Koebner phenomenon” is a trigger for PsA. The most common entheseal indices are the Spondyloarthritis Research Consortium of Canada (SPARCC) index; Leeds Enthesitis Index (LEI) and Maastricht Ankylosing Spondylitis Enthesitis Score (MASES).
Global assessment
Minimal disease activity (MDA) is a ‘state’ of disease activity in PsA, and is a simple index that is widely used clinically observationally.[23] A patient achieves MDA when 5 of 7 criteria are met, and very low disease activity (VLDA) is achieved when 7 of 7 criteria are met (Table 2).
| Table 2. Disease activity assessment tools for psoriatic arthritis | ||
| Tool | Measurement | Assessment |
| Global assessment of PsA | TJC ≤1 | MDA |
| SJC ≤1 | 5 of 7 criteria are met | |
| PASI ≤1 or body surface area ≤3% | VLDA | |
| Pain VAS* ≤1.5 cm | 7 of 7 criteria are met | |
| PGA VAS† ≤2 cm | ||
| HAQ-DI ≤0.5 | ||
| Tender entheseal points ≤1 | ||
| DAPSA (for peripheral arthritis) | 66SJC + 68TJC + PGA (cm) + pain (cm) + CRP mg/dL | Remission ≤4 |
| LDA >4 ≤14 | ||
| MDA >14 ≤28 | ||
| HDA >28 | ||
|
PsA = psoriatic arthritis; TJC = tender joint count; SJC = swollen joint count; PASI = psoriasis area and severity index; VAS = visual analogue scale; PGA = patient global assessment; HAQ-DI = health assessment questionnaire disability index; DAPSA = disease activity in PsA; CRP = C-reactive protein; MDA = minimal disease activity; VLDA = very low disease activity; LDA = low disease activity; HDA = high disease activity |
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Laboratory measures
Inflammatory markers such as erythrocyte sedimentation rate and C-reactive protein are elevated in only ~50% of patients with PsA, despite having active disease. These measures may, however, have prognostic value.[24,25]
Benitha, R., Maharaj, A. B., Makan, K., Potts, J., Lai, A., Carter, R., van Dam, M., & Hodkinson, B. (2024). South African Rheumatism and Arthritis Association 2024 guidelines for the management of peripheral spondyloarthritis. South African Medical Journal, 114(10), e2669.