When the Electromyography (EMG) and the Patient Disagree: Unraveling a Motor Neuron Disease Mimic With Small-Fiber Dysfunction.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by upper and lower motor neuron dysfunction. Electromyography (EMG) is central to its evaluation, but neurogenic abnormalities and fasciculations are not specific to ALS and must be interpreted within the clinical phenotype and disease trajectory. This study reports a 52-year-old man with an approximately eight-year history of intermittent muscle twitching, bilateral upper-limb tremor, muscular tightness and warmth, and asymmetric cutaneous hypersensitivity. An initial electrodiagnostic evaluation raised concern for diffuse motor neuron disease, despite preserved strength, normal gait, absence of muscle wasting, and lack of clear upper motor neuron signs. Extensive evaluation for inflammatory, autoimmune, metabolic, toxic, infectious, paraneoplastic, neuromuscular junction, and peripheral nerve hyperexcitability disorders was unrevealing. Serum creatine kinase was mildly and variably elevated, while aldolase and a comprehensive myositis panel were normal. Brain magnetic resonance imaging (MRI) demonstrated no supportive features of ALS. Sudomotor testing showed reduced electrochemical skin conductance (ESC) in the hands, supporting small-fiber/autonomic dysfunction in the context of prominent sensory symptoms. Repeat EMG, performed after interval follow-up with broad muscle sampling, demonstrated focal neurogenic abnormalities involving bilateral ulnar distributions and left L5-S1 radiculopathy but found no electrophysiological evidence of a neurodegenerative disorder. The patient was treated symptomatically with gabapentin and vitamin E and reported approximately 80% improvement after six weeks. This case highlights the importance of clinicophysiological correlation, disease trajectory, sensory phenomenology, and repeat electrophysiology when an initial EMG suggests motor neuron disease but the longitudinal clinical picture is discordant. It also illustrates how small-fiber dysfunction and focal neurogenic abnormalities may coexist and mimic a progressive motor neuron syndrome.