A 50-year-old female with MG presented with limb weakness and numbness, dragging gait, and no diurnal variation, and had a long-term use of low-dose corticosteroid. Spinal MRI from an external hospital showed cervical cord injury with edema, initially diagnosed as exacerbated MG with cervical spondylotic myelopathy, and surgery was recommended. The patient was admitted to our department for hospitalization and examination revealed dysarthria, bilateral ptosis, diplopia, sensory abnormalities at T6 level, and left lower limb muscle strength of V-. Spinal MRI showed C2-4 lesions, and myelitis could not be ruled out. Serum testing showed positive AQP4 antibody (1:32) and AChR-IgG (14.227 nmol/L). The patient was diagnosed with AQP4 antibody-positive NMOSD complicated by MG and cervical spondylosis, with EDSS score of 2 and ADL score of 5.

The patient received corticosteroid pulse therapy and pyridostigmine bromide, followed by inebilizumab. At discharge, EDSS score was 2, and ADL score was 2. Seven months later, the patient recovered well with EDSS and ADL scores of 0.

Clinicians should be vigilant in differentiating cervical spondylosis with cervical cord compression from NMOSD to avoid misdiagnosis and unnecessary surgery. NMOSD typically presents as long-segment that are centrally located, whereas cervical spondylosis with cervical cord compression often involves short segments, progressing from the compression site toward the center, with lesion size proportional to the degree of compression. AQP4 antibody-positive NMOSD and AChR antibody-positive MG are both IgG-mediated diseases that respond well to B-cell depletion therapy. In this case, inebilizumab achieved a "dual therapeutic effect."