Methotrexate Cutaneous Toxicity following a Single Dose of 10 mg in a Case of Chronic Plaque Psoriasis: A Possible Idiosyncratic Reaction.

Low-dose methotrexate is a well-tolerated and inexpensive systemic immunosuppressive agent used commonly in dermatology. However, several adverse events such as pancytopenia, pneumonitis, mucositis, and cutaneous ulcerations may develop during acute toxicity with dose-dependent or idiosyncratic mechanisms. Risk factors for methotrexate toxicity include advanced age, hypoalbuminemia, renal dysfunction, and concomitant drugs increasing the level of methotrexate in the body. We present a case of methotrexate toxicity presenting with classical features along with mucocutaneous side-effects, such as ulceration of psoriatic plaques and acral erythema, following a single dose of methotrexate.