Rheumatoid-type hand deformities in psoriatic arthritis: An illustrative case

Case presentation

A 65-year old female, with a background of psoriasis diagnosed two years before, presented with subacute inflammatory polyarthritis of the hand joints (predominantly proximal and distal interphalangeal joints (PIPJs and DIPJs)) of 1-month duration, associated with early morning stiffness lasting 45 min, associated joint swelling, and improvement with activity. On examination, she had active synovitis over multiple PIPJs and DIPJs with a tender joint count of six and a swollen joint count of four. Deformities were noted in the left hand, including a swan neck deformity of the index finger and a Boutonniere deformity of the middle finger (Fig. 1). Dermatological examination revealed well-defined erythematous plaques with silvery white scales over the dorsal aspects of the PIPJs and DIPJs (Fig. 2). Nail examination showed features suggestive of psoriatic nail involvement, including pitting and onycholysis. Examination of the left foot revealed hallux varus deformity (Fig. 3). There were no features suggestive of other seronegative spondylo-arthropathies, no history of inflammatory back pain, uveitis (eye redness or pain), oral ulcers, enthesitis, or dactylitis. Systemic examination was otherwise unremarkable. Based on the presence of inflammatory arthritis involving the PIPJs and DIPJs, associated cutaneous psoriasis, nail changes, and characteristic deformities, a diagnosis of psoriatic arthritis was considered. The diagnosis was supported by the classification for psoriatic arthritis (CASPAR) classification criteria. Rheumatoid arthritis (RA) was considered in the differential diagnosis; however, the presence of DIPJ involvement, absence of a classical symmetrical small joint pattern, with negative rheumatoid factor and anti cyclic citrulinated peptide antibody also negative made it less likely. Erosive osteoarthritis was also considered; however, the presence of inflammatory features such as prolonged morning stiffness, along with co-existing psoriasis and nail involvement, favoured psoriatic arthritis. Our patient was started on methotrexate as a disease-modifying agent along with ibuprofen for symptomatic relief. On regular follow-up, she showed significant clinical improvement, and at three months, was symptom-free on maintenance methotrexate therapy.

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Figure 1.

Left hand showing swan neck deformity in the index finger and boutonniere deformity in the middle finger.

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Figure 2.

Pink plaques with silvery white scale present over the dorsal surface of the PIPJs and DIPJs.

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Figure 3.

Left foot showing hallux varum deformity.

Discussion

Psoriatic arthritis (PsA) is a chronic inflammatory musculoskeletal disease associated with psoriasis and is classified under the seronegative spondylo-arthropathies. It develops in approximately 20–30% of patients with psoriasis and demonstrates heterogeneous patterns, including asymmetric oligoarthritis, symmetric polyarthritis, distal interphalangeal (DIP) predominant arthritis, axial disease, and arthritis mutilans. DIPJ involvement is considered a distinguishing feature of PsA and aids in differentiating it from RA, where DIPJs are typically spared. In our case, the co-existence of active psoriatic plaques over the dorsal interphalangeal joints and inflammatory tenderness of both PIPJs and DIPJs strongly favoured a diagnosis of PsA, consistent with established classification criteria such as CASPAR.^1,2

Psoriatic arthritis (PsA) encompasses five clinical patterns as described by Moll and Wright, with symmetric polyarticular (RA-like) disease being the second most common presentation. ³ This subtype can manifest with classical deformities such as swan neck and boutonnière deformities. Nevertheless, the development of such characteristic RA-type deformities in PsA is relatively infrequent, underscoring the clinical significance of their presence in our patient. Generally, it reflects chronic synovitis with ligamentous imbalance and structural damage. ⁴ Such presentations may pose a diagnostic challenge, particularly in elderly patients; however, the presence of cutaneous psoriasis and DIP involvement supports PsA over RA. Veale and Fearon have emphasised the phenotypic heterogeneity of PsA and its potential to resemble RA in certain subsets clinically. ⁵

The additional finding of hallux varum deformity suggests advanced structural involvement of the foot. While forefoot deformities are well described in inflammatory arthropathies, they are less frequently highlighted in PsA literature. Chronic inflammation, enthesitis, and capsuloligamentous imbalance may contribute to such deformities.^4,6 This case underscores the importance of thorough musculoskeletal examination in psoriasis patients presenting with joint symptoms, as PsA may manifest with RA – such as deformities, reinforcing the need for early diagnosis and timely initiation of disease-modifying therapy to prevent irreversible joint damage. ⁷