Objective: The sesamoid index was originally described as an aid to the diagnosis of acromegaly. We performed this study to assess the value of the thumb sesamoid index in the diagnosis of psoriatic arthropathy.
Design: Retrospective measurement of the sesamoid index (length x width of the medial thumb sesamoid), along with the age and sex were recorded for patients as described below. Patients with psoriasis were subdivided into those with or without radiographic evidence of hand arthropathy.
Patients: Fifty-nine consecutive patients attending rheumatology clinics with arthralgia and psoriasis were studied. Comparison groups with radiographic evidence of rheumatoid arthritis (52 patients), osteoarthritis (44) or normal hands (55) were also recorded.
Results: Twenty-one of 59 patients with psoriasis and arthropathy had a sesamoid index>40, compared with two of 52 with rheumatoid arthritis, none of 44 with osteoarthritis and none of 55 normals.
Conclusions: Psoriatic arthropathy is a recognised cause of bone enlargement, usually in the phalanges due to periostitis and proliferative enthesopathy. We have confirmed that psoriatic hand arthropathy can cause significant enlargement of the thumb sesamoids, a feature which is easily quantified and may assist diagnosis.