MRI-Negative Transverse Myelitis Revealing Seropositive Rheumatoid Arthritis in a Young Woman.

Transverse myelitis (TM) is an inflammatory disorder of the spinal cord often associated with autoimmune diseases, such as systemic lupus erythematosus (SLE) or neuromyelitis optica spectrum disorder (NMOSD); however, it is rarely linked to rheumatoid arthritis (RA). We present the case of a 28-year-old woman with subacute ascending numbness, lancinating pain, and bilateral lower extremity weakness resulting in significant functional impairment. Despite upper motor neuron signs on examination and supportive cerebrospinal fluid findings, including elevated gamma globulins and positive myelin basic protein, spinal MRI remained negative. The patient failed to improve with corticosteroids but showed a significant response to intravenous immunoglobulin. Electrophysiological studies indicated a central process, and serologic workup later revealed rheumatoid factor positivity. She was ultimately diagnosed with seropositive RA and started on certolizumab pegol. Alternative diagnoses, including multiple sclerosis (MS), NMOSD, Guillain-Barré syndrome, and compressive or ischemic myelopathy, were ruled out. This case highlights the diagnostic challenge of MRI-negative TM and its potential association with systemic autoimmune disease, specifically RA. It emphasizes the importance of clinical vigilance, early cerebrospinal fluid analysis, and prompt immunotherapy even in the absence of imaging abnormalities. Our findings broaden the neurologic spectrum of RA and support the role of infection-triggered immune dysregulation in autoimmune myelitis.