Michael D. Zhitnitsky, DO
Resident
Mayo Clinic
Rochester, Minnesota, United States
James B. Meiling, DO
Assistant Professor in Physical Medicine and Rehabilitation
Mayo Clinic
Rochester, Minnesota, United States
An 81-year-old left-handed male presented with acute left shoulder girdle pain following COVID-19 immunization. The pain was localized around his left shoulder girdle and neck. As the pain subsided, he developed weakness in the left proximal arm. Examination revealed profound weakness in the left supraspinatus, infraspinatus, deltoid, biceps brachii, brachioradialis muscles, and mildly in the thenar muscles. Hyperreflexia of the left biceps and fasciculations in left deltoid and biceps were noted, raising concerns for amyotrophic lateral sclerosis (ALS). MRI cervical spine showed severe spinal canal narrowing at C4-C5 without cord abnormality. EMG showed ongoing denervation and marked reduced recruitment of large motor unit potentials isolated to the left MCN, axillary, and suprascapular nerve distributions. NMUS demonstrated focal fascicular enlargement of the proximal MCN, further confirming the diagnosis of PTS rather than ALS.
Discussions: PTS typically presents with severe, acute shoulder and arm pain, followed by weakness and muscle atrophy. It can mimic several disorders, including cervical myelopathy, cervical radiculopathy, musculoskeletal shoulder conditions, or even a lower motor neuron predominant ALS. When used with EMG, NMUS assists in distinguishing PTS from other conditions by detecting focal nerve or fascicle enlargement, one of several pathognomonic signs of PTS. In contrast, NMUS of nerves in ALS does not show nerve or fascicle enlargement.
Conclusions:
NMUS is an underutilized yet valuable tool that may be used to evaluate neuromuscular disorders, especially when physical examination and electrodiagnostic testing are inconclusive. Its ability to provide detailed visualization of peripheral nerves makes it an essential component of the diagnostic process for conditions such as PTS.
