Background Monoarthritis is the most common form of arthritis in the general practice. In primary care an arthritis of the first metatarsophalangeal (MTP) joint is almost always considered as gout. Gout is the most frequent cause of a monoarthritis that affects the first MTP joint, but it is unknown which other forms of arthritis occur in the first MTP joint.^1-2-3

Objectives The aims of this study are firstly to determine which other forms of monoarthritis occur in the first MTP joint, and secondly to identify the clinical differences between patients with an arthritis of the first MTP joint caused by gout and those not caused by gout.

Methods In this observational follow-up study 159 patients with a monoarthritis of the first MTP joint have been included. These patients were referred by their general practitioner (GP) to the Department of Rheumatology of Rijnstate Hospital, The Netherlands, because of a clinical trial regarding the treatment of an acute gout attack.⁴ Within 24 hours of presentation to the GP, the patients were examined by a rheumatologist. Clinical variables were collected. The synovial fluid of the affected MTP-1 joints was obtained and analyzed for the presence of MSU crystals. Thereafter, patients with undifferentiated monoarthritis (n=24) were followed-up by their GPs. 7 years later, in 2012, the GPs were asked for additional information about the course of the disease. In addition, the medical hospital records have been researched whether there eventually was established a definite diagnosis.

Results After a mean follow-up period of 7 years 36 of the 159 patients (23%) with MTP-1 arthritis did not have gout. 24 of them had no diagnosis and 12 patients had a different diagnosis than gout, namely rheumatoid arthritis, osteoarthritis, psoriatic arthritis, pseudogout, arthritis with an inflammatory bowel disease, bunion, palindromic rheumatism, IgM rheumatoid factor (RF) positive arthritis, and IgM RF and ACPA negative, ANA positive arthritis. The characteristics which are statistically significant more present in patients with gout are male sex, a previous arthritis, the use of diuretics, the use of cardiovascular or antihypertensive drugs, hypertension or cardiovascular disease, beer consumption, BMI >25 kg/m², serum uric acid >0.35 mmol/L, serum creatinine >105 mcmol/L, glomerular filtration rate <60 mL/min, and C-reactive protein >10mg/L (p<0,05).

Conclusions Gout is a prominent but certainly not an exclusive cause of MTP-1 arthritis. In almost a quarter of the patients with a MTP-1 arthritis the cause is different than gout. In these patients the arthritis is mostly an expression of a transient undifferentiated arthritis or a different persistent rheumatic disease. We advocate aspiration of MTP-1 arthritis in order to differentiate gout from other forms of MTP-1 arthritis, in particular when a valid diagnosis has therapeutic or prognostic consequences.

References

1. Huskisson, E. C., et al. (1972). “Pseudopodagra. Differential diagnosis of gout.” Lancet 2(7771): 269-71.

2. Ma, L., A. Cranney, et al. (2009). “Acute monoarthritis: what is the cause of my patient’s painful swollen joint?” Cmaj 180(1): 59-65.

3. Velilla-Moliner, J., et al. (2004). “Podagra, is it always gout?” Am J Emerg Med 22(4): 320-1.

4. Janssens, H. J., et al. (2008). “Use of oral prednisolone or naproxen for the treatment of gout arthritis: a double-blind, randomised equivalence trial.” Lancet 371(9627): 1854-60.

Disclosure of Interest None Declared