A Case of Suspected Breast Cancer Metastasis to Brachial Plexus Detected by Magnetic Resonance Neurography.

Metastasis of breast cancer is often detected through a long-term course and difficult to diagnose. We report a case of brachial plexopathy suspected to be the initial lesion of breast cancer metastasis, which was only detected by magnetic resonance (MR) neurography. A 61-year-old woman was admitted to our hospital within 2 years after operation for breast cancer because of progressive dysesthesia and motor weakness initially in the upper limb on the affected side and subsequently on the contralateral side. Enhanced computed tomography, axillary lymph node echo, gallium scintigraphy, and short tau inversion recovery MR images showed no abnormalities. MR neurography revealed a swollen region in the left brachial plexus. We suspected neuralgic amyotrophy and initiated treatment with intravenous immunoglobulin therapy and steroid therapy. However, there was no improvement, and the progression of motor weakness in the bilateral lower limbs appeared over 4 years. Concomitant elevation of carbohydrate antigen 15-3 level (58.9 U/ml) led us to suspect breast cancer metastasis, which was associated with the worsening of neurological findings, although gallium scintigraphy and bone scintigraphy showed no inflammatory and metastatic lesions. Swelling of the cauda equina in enhanced lumbar MR imaging and abnormal accumulation at the brachial plexus and cervical spinal cord in positron-emission tomography were newly detected contrary to the normal findings on the gallium scintigraphy, which suggested cerebrospinal fluid seeding. We suspected breast cancer metastasis about the initial brachial plexopathy based on the clinical course. MR neurography may be a helpful tool to detect metastatic lesion, especially in nerve roots.