Psoriatic arthropathy

Definition and classification. A seronegative inflammatory arthritis associated with psoriasis, belonging to the spondyloarthropathy family. Moll and Wright's five patterns: (i) asymmetric oligoarthritis, (ii) symmetric polyarthritis (RA-like), (iii) distal interphalangeal (DIP) predominant, (iv) spondylitis/sacroiliitis, (v) arthritis mutilans.

Clinical features. Dactylitis ("sausage digit"), enthesitis (Achilles tendon, plantar fascia), DIP joint involvement with nail disease (pitting, onycholysis, subungual hyperkeratosis, oil-drop sign), inflammatory back pain, and extra-articular features such as uveitis. Skin disease usually precedes the arthritis. Elderly-onset psoriatic arthritis tends to be more polyarticular, more acutely inflammatory (higher ESR/CRP) and more erosive than younger-onset disease.

Investigations. RF and anti-CCP negative; ESR and CRP raised; uric acid may be raised (a source of diagnostic confusion). Radiology: erosions with adjacent new bone formation, the "pencil-in-cup" deformity, periostitis, ankylosis and asymmetric sacroiliitis. Diagnosis is made with the CASPAR criteria; the PEST questionnaire is used to screen psoriasis patients.

Differential diagnosis in the older adult. Rheumatoid arthritis (symmetric, seropositive, spares the DIP joints), erosive/nodal osteoarthritis of the DIP joints (Heberden's nodes — a major overlap in this age group), gout (common in older men on diuretics), pseudogout, and reactive arthritis.

Management principles. Treat-to-target, aiming for minimal disease activity. Physiotherapy, graded exercise, weight reduction, smoking cessation and active cardiovascular risk reduction — psoriatic arthritis carries a high burden of metabolic syndrome, diabetes and cardiovascular disease. Local corticosteroid injection for a single inflamed joint or enthesis. NSAIDs help mild peripheral disease but are relatively contraindicated in older adults (renal impairment, GI bleeding, hypertension, heart failure — Beers criteria).

Drug therapy. Conventional synthetic DMARDs — methotrexate (monitor renal function, reduce dose for the age-related fall in GFR, give folate), leflunomide or sulfasalazine for peripheral disease; csDMARDs do not work for axial disease. Biologics for inadequate response or axial involvement: TNF inhibitors, IL-17 inhibitors (secukinumab, ixekizumab), IL-12/23 (ustekinumab) and IL-23 inhibitors (guselkumab, risankizumab). Targeted synthetic agents: apremilast (PDE4 inhibitor — no laboratory monitoring, well tolerated in frail older adults) and JAK inhibitors (tofacitinib, upadacitinib). Screen for latent tuberculosis and hepatitis B before any biologic — essential in India.

Following the ORAL Surveillance safety data, current EULAR and GRAPPA recommendations advise that JAK inhibitors should not be used first-line in patients over 65 or with cardiovascular risk factors, a smoking history or malignancy risk, because of increased major adverse cardiovascular events, venous thromboembolism, malignancy and herpes zoster. IL-17 and IL-23 inhibitors are preferred in this group — bimekizumab (dual IL-17A/F blockade) was approved for psoriatic arthritis in 2023–24 and guselkumab has strong axial and peripheral data — while apremilast remains the low-monitoring option for frail older adults with mild disease. If this appears as a 15-mark question, add: pathogenesis (IL-23/IL-17 axis, HLA-B27 in axial disease, the enthesis as the primary site); full CASPAR criteria with scoring; the six GRAPPA domains (peripheral arthritis, axial disease, enthesitis, dactylitis, skin, nails) and domain-based drug selection; a comparison table of PsA versus RA versus osteoarthritis versus gout in the older patient; comorbidity screening (metabolic syndrome, fatty liver, depression, uveitis, inflammatory bowel disease); and vaccination and TB screening before immunosuppression in the Indian context.