A 41-year-old healthy man from Guinea-Bissau with severe psoriasis and psoriasis area and severity index of 38 initiated weekly treatment with methotrexate (20 mg per os). Four days later, he presented with painful exudative skin erosions covering some psoriatic plaques (Fig. 1).
Previous laboratory tests were normal, but after the drug was initiated showed haemoglobin 12.5 g/dL, leucopenia 1.6x109/L (66% neutrophils), raised erythrocyte sedimentation rate (69 mm/h) and raised C-reactive protein (22.1 mg/dL). Serum methotrexate level was below 0.04 μmol/L.

Full paper available here.