Arthritis of the first metatarsophalangeal joint is not always gout: a prospective cohort study in primary care patients

OBJECTIVES: Arthritis of the first metatarsophalangeal joint has been considered pathognomonic for gout, but it is unknown how frequently other forms of arthritis occur in this joint. The aims were to determine the validity of the general practitioner's clinical diagnosis using joint fluid analysis as the reference test, the prevalence of other diagnoses than gout, and the signs and symptoms that discriminate between gout and non-gout patients. METHODS: This prospective cohort study comprised primary care patients with monoarthritis of the first metatarsophalangeal joint. After patient recruitment by general practitioners, patients' characteristics were collected by a rheumatologist. Joint fluid was analyzed for the presence of monosodium urate-crystals. If crystals were absent, patients entered a follow-up period of 6 years, or until a definite diagnosis. If during follow-up crystals were identified, the patient was classified as already having gout at baseline assessment. RESULTS: One hundred and fifty-nine primary care patients were included. At baseline the clinical diagnosis was gout in 98%. The positive and negative predictive values of the diagnosis of gout were 0.79 and 0.75, respectively. After follow-up 77% had gout, 8% had another rheumatic disease, and 15% had a transient unspecified monoarthritis. Gout patients had discriminating signs and symptoms from non-gout patients. CONCLUSIONS: Gout is an important but certainly not an exclusive cause of arthritis of the first metatarsophalangeal joint