Baumer P, Kele H, Xia A, et al. Posterior Interosseous Neuropathy: Supinator Syndrome vs. Fascicular Radial Neuropathy.
Neurology 2016; 87: 1884-91.
Submitted by David B. Rosenfield, MD, News Science Editorial Board
The radial nerve (RN) divides proximal to the elbow into a cutaneous sensory branch and a deep motor branch that pierces the supinator muscle at the level of the elbow and then becomes the posterior interosseous nerve (PIN). Lesions of the RN or its motor branch can occur at any point along its course attributable to different causes, including trauma, tumor, compression or inflammation. One frequent cause of PIN is compression at the supinator muscle, PIN syndrome.
The authors performed MRI assessment on 19 patients with PIN lesions, examining the upper arm and elbow. They noted only three had imaging evidence for a focal neuropathy at the entry of the radial nerve deep branch into the supinator muscle, and the other 16 had imaging evidence for proximal radial nerve compromise in the upper arm, usually 4-12 cm proximal to the humero-radial joint. 75% of these lesions followed a specific somatotopic pattern involving only those fascicles that would form distally the PIN.
The authors conclude PIN syndrome is not necessarily caused by focal compression at the supinator muscle, but instead frequently results from partial fascicular lesion of the radial nerve trunk in the upper arm level, and that neuro-imaging should be considered a complementary diagnostic method in PIN syndrome.
This is an excellent review of PIN syndrome and radial nerve anatomy. Compression in the supinator was not the most frequently identified lesion site in this study. Clinical exam and electrodiagnostic studies can be helpful, but adjunct testing such as MRI may help to localize the lesion. It should be noted that surgical confirmation of the nerve lesion was not noted in this study.
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