What happened, in summary

A 51-year-old woman was hospitalized with severe nausea, vomiting and fatigue. During the evaluation, CT unexpectedly found several nodules in her left breast. Her symptoms later progressed to leg weakness, numbness and difficulty urinating, and spinal imaging showed extensive transverse myelitis. Testing confirmed neuromyelitis optica spectrum disorder with AQP4 antibodies.

A biopsy of a left-breast tumor showed invasive ductal carcinoma that was estrogen-receptor positive, progesterone-receptor positive and HER2-negative. The tumor cells also expressed AQP4, supporting the conclusion that the neurologic illness was a rare paraneoplastic complication of her breast cancer.

She underwent total left mastectomy with lymph-node dissection. Surgical pathology confirmed poorly differentiated invasive ductal carcinoma, and the cancer was Stage III. Treatment for the neurologic disorder improved the severe nausea and vomiting and stopped further rapid neurologic decline. At discharge for rehabilitation, she remained wheelchair-dependent but no longer had the intractable gastrointestinal symptoms that had led to her hospitalization.