Perineural Spread of Melanoma to the Brachial Plexus: Identifying the Anatomic Pathway(s)

Background: Perineural spread of melanoma is a well-known mechanism of metastasis in cases involving cranial nerves. Brachial plexus involvement is rare, and the pathway is unknown. Methods: A retrospective review of the Mayo Clinic database was performed to identify patients with a history of melanoma and brachial plexus compromise treated between 1994 and 2017. Inclusion criteria were a history of melanoma, a clinical diagnosis of brachial plexopathy, radiologic features consistent with perineural spread, and biopsy of melanoma within nerves. Results: We identified 42 patients (24 men and 18 women; median age, 61 years; range, 37–84 years) with a history of melanoma and brachial plexopathy. On a review of clinical information, 2 cases met our inclusion criteria. Both patients presented with progressive brachial plexopathy, and imaging studies revealed features consistent with perineural spread. In 40 excluded patients, brachial plexopathy was caused by metastasis to axillary lymph nodes (n = 11), trauma (n = 8), post-surgical sequelae (n = 7), tumors other than melanoma (n = 5), inflammation (n = 5), radiation (n = 2), a combination of radiation and postsurgical changes (n = 1), and radiculopathy (n = 1). Conclusions: The 2 patients identified had similar clinical and radiologic features. We believe that there is a pattern of perineural spread to the brachial plexus through the cervical plexus. A literature review identified several recently published cases demonstrating an analogous mechanism of melanoma spread involving upper cervical nerves, supporting our proposed pathway.