Abstract
Methotrexate is a commonly employed folate antagonist used as a disease modifying antirheumatic drug. It is recommended by the European League Against Rheumatism Guidelines as an add-on therapy for the treatment of polymyalgia rheumatica. Lymphoproliferative disease developing during methotrexate treatment is recognised as methotrexate-associated lymphoproliferative disorder. We describe a patient with polymyalgia rheumatica on long-term methotrexate treatment presenting with double vision and systemic symptoms concerning for giant cell arteritis. Two months prior, she had noticed a mass of the right nasal dorsum. Neuroimaging showed several lesions of the nasal cavity and a clival lesion. Nasal cavity biopsy revealed diffuse large B-cell lymphoma, and FDG-PET/CT 3 weeks after methotrexate cessation showed significant interval disease regression, confirming the diagnosis of methotrexate-associated lymphoproliferative disorder. Follow-up FDG-PET/CT 4 months after methotrexate cessation showed complete radiological regression of lymphoproliferative lesions. The cumulative incidence of methotrexate-associated lymphoproliferative disorder in patients with rheumatoid arthritis treated with methotrexate has been reported to be up to 4.7% at 10 years in a retrospective study. Cessation of methotrexate resulted in spontaneous regression in 59% of patients. It is important to include methotrexate-associated lymphoproliferative disorder on the differential diagnosis for patients on long-term methotrexate treatment who present with neuro-ophthalmic symptoms and signs as tissue diagnosis prior to commencing steroid treatment is essential to secure the diagnosis and guide treatment.