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

Abstract

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.

Introduction

Acute gout occurring in the first metatarsophalangeal (MTP-1) joint was already among the earliest diseases to be recognized as podagra [1]. Nowadays MTP-1 arthritis is still considered to be the hallmark of gout.

Monoarthritis is a common form of arthritis in primary care. The differential diagnosis of monoarthritis is extensive. In at least 20% of the primary care patients it is not possible to reach a definitive diagnosis, i.e. an unspecified monoarthritis [2]. Within the group of monoarthritis gout is the most prevalent diagnosis (57%) [2]. One to two percent of the population has been identified as having gout [3]. The prevalence of MTP-1 arthritis in patients with monoarthritis is about 40% [2]. The initial attack of gout affects the MTP-1 joint in 56–78% of the patients. This joint is involved at some point in the course of gout in 59–89% [4], [5].

Despite the fact that gout is the most frequent cause of a monoarthritis and that gout occurs most often in the first MTP joint, it is unknown how often other forms of arthritis occur in MTP-1. A definitive diagnosis is important because of therapeutic, prognostic and comorbid, i.e. cardiovascular [6], [7], [8], consequences. The consequences of the wrong diagnosis of gout are incorrect information to the patient, incorrect estimation of the prognosis, and prescription of incorrect therapeutic measures. The latter implies useless uric acid lowering therapy, and failure to offer anti-rheumatic therapy in case of rheumatoid arthritis, psoriatic arthritis and osteoarthritis.

The first aim of this study was to determine the validity of the general practitioner's (GP's) clinical diagnosis gout in the MTP-1 joint using the identification of monosodium urate (MSU)-crystals in joint fluid as the reference test. Secondly, to determine the prevalence of other forms of monoarthritis in the MTP-1 joint. The third aim was to identify the clinical signs and symptoms that discriminate between patients with and without gout.