Background There is controversy about methotrexate (MTX) as a therapy of giant cell arteritis (GCA).

Objectives The objective is to present a case who developed GCA during therapy with MTX in association with corticosteroids for rheumatoid arthritis.

Methods A 66-year-old-woman was diagnosed in 1998 as seronegative rheumatoid arthritis involving knee, shoulder and wrist joints. ESR was 46 mm/1 h, synovial fluid contained 29 G/L leukocytes but no crystals were observed. The patient was treated with MTX at a weekly dose of 7,5 mg, dosage increased to 10 mg/week in February 2000. In addition, she received prednisone 5 mg per day. In November 2000 she started to feel some weakness and to suffer from frontal headaches. The ESR was 120 mm/1 h, CRP 121 mg/l and Hb 80 g/L. The biopsied right temporal artery, which was tender and indurated, demonstrated GCA. The internal elastic lamina was fragmented; there were infiltrates of histiocytes, lymphocytes and giant cells and the lumen was in some places occluded.

Conclusion In this case, occurrence of GCA was not prevented by MTX therapy. This suggests that MTX at an average dose is probably insufficient to prevent or treat this disease.