Clinical Reasoning: A Patient With Progressive Sensory Neuropathy: Using Nerve Ultrasound and Skin Biopsy to Refine Diagnostic Reasoning.

A 74-year-old man presented with a 5-year history of progressive feet numbness followed by gait unsteadiness. Neurologic examination revealed absent tendon reflexes, markedly reduced vibration sense in the lower limbs with sensory ataxia, and preserved motor strength. The clinical picture was consistent with a chronic sensory-predominant neuropathy causing sensory ataxia. Nerve conduction studies demonstrated a sensory axonal polyneuropathy with absent sensory nerve action potentials and preserved compound motor action potentials. Extensive screening for potential acquired causes of polyneuropathy (including metabolic, autoimmune, infectious, and toxic etiologies) yielded negative results, and the condition was initially classified as an idiopathic sensory polyneuropathy. Nerve ultrasound showed bilateral reduction of upper-limb nerve cross-sectional area, predominantly in the median and ulnar nerves at the forearm. Skin biopsy revealed loss of somatic intraepidermal fibers with relative preservation of autonomic innervation. This multimodal assessment refined diagnostic reasoning, shortened the diagnostic odyssey associated with establishing an etiologic diagnosis in idiopathic axonal sensory polyneuropathy, and prompted targeted genetic testing. Such an approach may improve diagnostic yield in idiopathic sensory-predominant axonal polyneuropathies.