Methotrexate-associated lymphoproliferative disorder of the thoracic spine in a patient with rheumatoid arthritis receiving methotrexate: a case report.

Methotrexate-associated lymphoproliferative disorder is recognized as a lymphoma that occurs following methotrexate administration. The lesion of the spine is extremely rare, and only one case of lesion in the lumbar spine has been reported so far. Here, we present a case of methotrexate-associated lymphoproliferative disorder of the thoracic spine in a 54-year-old woman with rheumatoid arthritis. The lesion formed an extra-skeletal tumor mass from lateral to the vertebral body to the paravertebral muscle extending posterior to the epidural space without bone destruction. Magnetic resonance imaging showed low signal intensities on both T1- and T2-weighted images and high signal intensity with short-tau inversion recovery. These radiological findings were similar to those for primary spinal lymphoma. The lesion rapidly paralyzed the patient, forcing her to be treated with posterior spinal decompression. The lesion could not be resected because it adhered to the dura. Following the histopathological diagnosis as methotrexate-associated lymphoproliferative disorder, methotrexate administration was terminated. The remaining mass lesion showed complete regression within 6 months. Methotrexate-associated lymphoproliferative disorder, which could be cured by the discontinuation of methotrexate, should be considered a differential diagnosis in spinal lesion cases showing lymphoma-like appearance with methotrexate treatment to avoid unnecessary treatments.