Digital clubbing, recognized by Hippocrates in the fifth century BC, is the outward hallmark of pulmonary hypertrophic osteoarthropathy, a clinical constellation that develops secondary to various acquired diseases, especially intrathoracic neoplasm. The pathogenesis of clubbing and hypertrophic osteoarthropathy has hitherto been poorly understood, but a clinically indistinguishable primary (idiopathic) form of hypertrophic osteoarthropathy (PHO) is recognized. This familial disorder can cause diagnostic confusion, as well as significant disability. By autozygosity methods, we mapped PHO to chromosome 4q33-q34 and identified mutations in HPGD, encoding 15-hydroxyprostaglandin dehydrogenase, the main enzyme of prostaglandin degradation. Homozygous individuals develop PHO secondary to chronically elevated prostaglandin E(2) levels. Heterozygous relatives also show milder biochemical and clinical manifestations. These findings not only suggest therapies for PHO, but also imply that clubbing secondary to other pathologies may be prostaglandin mediated. Testing for HPGD mutations and biochemical testing for HPGD deficiency in patients with unexplained clubbing might help to obviate extensive searches for occult pathology.

Objective. To determine the prevalence of psoriatic arthritis (PsA) using the ClASsification criteria for Psoriatic ARthritis (CASPAR) for classification. Methods. People with psoriasis were identified from the computerized morbidity indices of 2 large UK general practices, total population 22,500. Questionnaires were mailed to all 633 patients thus identified. Of the respondents, a 50% sample was assessed clinically and a proportion had blood samples and radiographs taken. Patients labeled as having psoriasis were also cross-referenced with a local secondary care morbidity index for PsA and rheumatoid arthritis. Figures for the prevalence of PsA were estimated from these data. Results. One hundred sixty-eight questionnaires were returned (response rate 27%) and 93 people (55% of questionnaire respondents) were examined. Of these 93 people, 12 (4 of whom were cross-referenced to the hospital database) were thought to have PsA clinically, all fulfilling the CASPAR criteria for PsA. Six of the 93 examined patients did not have psoriasis or a family history of psoriasis and had no historical features or clinical signs of psoriasis on interview and examination. Extrapolating from the data of those people actually examined, the estimated (corrected) prevalence was 13.8% (95% confidence interval 7.1-24.1%). Conclusion. The estimated prevalence of PsA in this population, using the CASPAR criteria, was 13.8%. Misclassification of psoriasis and arthritis, and response bias, indicate that this is probably an overestimate.

Objective. To assess the sensitivity and specificity of the Classification of Psoriatic Arthritis (CASPAR) Study Group criteria in early psoriatic arthritis (PsA) and to compare them with the sensitivity and specificity of the Moll and Wright criteria.Methods. The CASPAR Study Group criteria were applied to patients with early PsA (<24 months symptom duration) and to control patients with other newonset inflammatory arthritides. Both groups were naive to all disease-modifying antirheumatic drugs. The gold standard diagnosis was confirmed by the consulting rheumatologist using radiography and magnetic resonance imaging where required. Proportions of patients and control patients meeting the criteria were compared using McNemar's tests.Results. We recruited a total of 111 patients with early PsA and 111 control patients with other forms of inflammatory arthritis (82 with rheumatoid arthritis, 13 with undifferentiated arthritis, 9 with spondylarthritis, 4 with inflammatory osteoarthritis, and 3 with crystal arthritis) to the study. The sensitivity of the CASPAR Study Group criteria in classifying early PsA was 87.4% compared to 80.2% for the Moll and Wright criteria. The specificity for both criteria was 99.1%. When considering different cut points for the CASPAR Study Group criteria, the best cut point for classification remained a score of >3 as in the original CASPAR Study Group analysis. Considering a score of >2 gave a higher sensitivity of 99.1% but resulted in a drop in specificity to 94.6%. Regression analysis determined that psoriasis and rheumatoid factor negativity were the most important features that differentiated PsA, followed by nail psoriasis and current or previous dactylitis.Conclusion. The CASPAR Study Group criteria are more sensitive than the Moll and Wright criteria in classifying early PsA. Although their sensitivity for early PsA is lower than that for established disease, the CASPAR Study Group criteria are valid for use as inclusion criteria for trials in early PsA.

Objective. To compare scores for the Leeds enthesitis index in psoriatic arthritis and rheumatoid arthritis using clinical assessment and ultrasonography (US). Design. Swelling and tenderness of the enthesis was assessed at six sites: lateral epicondyles of humerus (LE), medial condyles of femur (MC), and the insertion of the Achilles tendon (AT). US assessed “inflammatory activity” (power Doppler signal, oedema, tendon thickening, and bursal swelling) and “damage” (erosions and enthesophytes). Results. 94 patients were included, 71 with PsA and 23 with RA. The patients with RA were significantly older (PsA 47.6 years; RA 62.6 years; (mean difference in ages =15.0 years, 95% CI 9.3–20.7 years)). US scores were higher in RA at the LE, significantly so for the “damage” scores. No differences between RA and PsA were seen at the other sites. As a result, the odds ratio for PsA, given an US score above the median, was 0.41 (0.13–1.03). However, using the clinical score, the odds ratio for PsA was 2.16 (0.81–5.70). Conclusions. Although clinical scores of enthesitis are greater in PsA compared to RA, US enthesitis scores did not distinguish between RA and PsA. This may in part be due to more frequent juxta-articular involvement in RA and in part due to the older age of the subjects with RA.