Acute severe cutaneous methotrexate toxicity in a patient with rheumatoid arthritis: Report of a rare side effect

Background: Skin lesions due to acute methotrexate (MTX) toxicity are rare. The majority of cases of cutaneous MTX toxicity have been reported in patients with psoriasis, exceptionally in patients with rheumatoid arthritis (RA). We report a case of RA who had an acute severe cutaneous MTX toxicity and its management. Case presentation: A 59 year old woman who has been followed up in Rheumatology department in Farhat Hached Hospital in Sousse in Tunisia since 2005 for RA. Since 2005 initially, she was treated with MTX at a dose of 10 mg/week orally that changed in 2014 to the injection route because of gastric intolerance. She also received oral corticosteroids (prednisone: 10 mg/day). In January 2017, she had mucosal and cutaneous erosions, post-bullous affecting the face mostly cheeks and subciliary arches and the forearms. A cutaneous biopsy was performed and showed a histological appearance compatible with photo-aggravated toxiderma with an eroded epidermis, keratinocytic necrosis and the presence of numerous eosinophils in the dermis which is elastosic. The Direct Immunofluorescence study was negative. Based on clinical and histological data, the diagnosis of acute severe cutaneous MTX toxicity was suspected. The patient recovered following MTX withdrawal and using a cicatrizing cream after a duration of 5 months. Treatment with Tocilizumab was started in March 2017. Conclusion: Although MTX is an option of great therapeutic value for RA. Rheumatologists and Dermatologists need to be alert to the possibility of cutaneous adverse events associated with MTX therapy. Keywords: Methotrexate, Rheumatoid arthritis, Cutaneous toxicity, Cutaneous biops