LAUSR

Nerve biopsies are often the most definitive test for the diagnosis of uncommon neurologic dysfunction. Historically, nontargeted biopsies of distal cutaneous (sensory) nerves (e.g., sural nerve) have been performed widely due to their expendable nature, accessibility, and ease of surgery, but they have had a relatively low yield (Hart et al., 2013). Nontargeted biopsy of motor nerve branches (e.g., obturator nerve (Riva et al., 2011), nerve to pronator teres (Dy et al., 2012), and superficial fibular (peroneal) nerve (D’Amico and Winfree, 2017)), has also been occasionally utilized with some early success. Fifteen years ago, targeted fascicular biopsy of a major (mixed) peripheral nerve was introduced as a new technique whereby pathology is localized using a combination of careful clinical examination, electrophysiological studies and focused nerve-based imaging. MRI targeted fascicular biopsy increased the diagnostic yield from 20%-50% to 74%-85% (Capek et al., 2015; Laumonerie et al., 2017). While the risk associated with this procedure at a tertiary care facility has been acceptably low, the procedure of performing a biopsy of a major nerve or plexus has not yet been widely adopted. Recently, this targeted technique has been refined to biopsy cutaneous nerves in select cases (Marek et al., 2017) and proposed as a safer and easier alternative to targeted fascicular biopsy. In one of these cases, pathology was confirmed by both a targeted cutaneous branch and a motor branch (nerve to the subclavius muscle). In this article, several cases are presented to extend this diagnostic approach by targeting a motor branch. The goal of targeting smaller sensory and motor branches is to minimize risk of worsening neurologic function secondary to biopsy, while still providing enough histopathological tissue to be diagnostic.