Ultrasonographic findings of proximal median neuropathy: A case series of suspected distal neuralgic amyotrophy

Spontaneous anterior interosseous nerve (AIN) palsy develops following the resolution of nerve pain, which may be considered as distal neuralgic amyotrophy. NA is assumed to have a complex etiology, but an autoimmune mechanism is likely involved. However, precise assessment of the lesion is challenging. We examined five consecutive patients with suspected spontaneous AIN palsy using ultrasonography. On electromyography, all patients exhibited denervation potentials in the muscles, not only in the AIN territory, but also in the proximal median nerve territory (e.g., the flexor carpi radialis or pronator teres). Ultrasonography of the median nerve demonstrated neural swelling at the proximal side of the medial epicondyle in four patients and an hourglass-like constriction of the nerve fascicle in three patients. Four patients were diagnosed with distal neuralgic amyotrophy; of these, three received intravenous immunoglobulin administration, but only limited beneficial effect was achieved in one patient with early stage disease. One patient showed significant median nerve hypertrophy on ultrasonography and was diagnosed with neurolymphomatosis following the detection of malignant lymphoma during a systemic survey. Our experience demonstrates that ultrasonography for proximal median neuropathy presenting as AIN palsy may be useful for the accurate lesion assessment.