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Severe Pancytopenia Associated with Low-Dose Methotrexate Therapy for Rheumatoid Arthritis

OBJECTIVE: To report the occurrence of severe pancytopenia associated with low-dose methotrexate (MTX) therapy for rheumatoid arthritis. CASE SUMMARY: Two patients developed severe pancytopenia after 10 days (cumulative dose 15 mg) and 23 months (cumulative dose 1030 mg), respectively, of low-dose MTX therapy for rheumatoid arthritis. Both patients had renal impairment. One died and the other recovered completely. DISCUSSION: Pancytopenia is a rare adverse effect of low-dose oral MTX therapy. The exact mechanism for development of pancytopenia is unknown, although it is likely that several factors play a role. The most important risk factor for MTX toxicity is impaired renal function. This adverse effect may occur at any time during MTX therapy. CONCLUSIONS: Severe pancytopenia associated with low-dose MTX therapy for rheumatoid arthritis is a potentially serious complication that may occur at any time during therapy. This adverse effect is more likely to occur in patients with renal impairment.