Methotrexate-Associated Lymphoproliferative Disease of the Thoracic Spine Misdiagnosed as Metastatic Spinal Tumor: A Case Report.

Methotrexate (MTX) is increasingly used in the treatment of rheumatoid arthritis. Many recent reports have identified MTX-related lymphoproliferative disorder (MTX-LPD) as lymphoma that develops during MTX therapy. However, spinal lesions, which are extremely rare, can be misdiagnosed as spinal metastases or pyogenic spondylitis. Here, we describe a 69-year-old man with rheumatoid arthritis who had MTX-LPD of the thoracic spine. He complained of back pain and weakness in the bilateral iliopsoas muscle. A radiographical assessment by his previous physician revealed the cause to be a spinal tumor. They performed posterior spinal decompression and fixation, and a pathological examination revealed only inflammatory changes, necrosis, and increased collagen fiber growth, with no evidence of malignancy. Nevertheless, magnetic resonance imaging two weeks after the surgery showed an increase in the size of the spinal tumor. When the lesion paralyzed the patient soon afterward, the physician considered that a total en bloc spondylectomy was necessary and referred the patient to our hospital. MTX-LPD was suspected because of a history of MTX administration, and a biopsy, posterior spinal decompression, and fixation were performed again. Following the histopathological diagnosis of the tumor as MTX-LPD, MTX administration was terminated. Three months following surgery, the tumors' removal was confirmed. Because MTX-LPD can be treated with MTX withdrawal, correct diagnoses should be made, and unnecessary treatments avoided.