348 - Neuromuscular ultrasound assists in the diagnoses of ulnar neuropathy in a patient with spinal muscular atrophy

Case Diagnosis: Ulnar neuropathy at the elbow

Case Description: A 63-year-old female with spinal muscular atrophy (SMA) type 3 presented to the neurology clinic for right elbow pain with subsequent development of gradually worsening right hand weakness that had progressed over two months. She denied neck pain, numbness, or tingling in the hand. On examination, she had diffuse atrophy due to her history of SMA, however she had worsening weakness in right 5^th digit abduction than previously noted. She was referred for electrodiagnostic testing. Electromyography (EMG) showed evidence of chronic end-stage neurogenic change throughout the right arm, consistent with history of SMA, and was unable to rule out superimposed right ulnar neuropathy given the inability to obtain proximal motor nerve conduction responses. It was recommended that she pursue neuromuscular ultrasound testing of the right ulnar nerve, which demonstrated evidence of entrapment neuropathy at the retrocondylar groove. Her wheelchair was adjusted to prevent elbow compression and her symptoms are improving.

Discussions: SMA is a degenerative lower motor neuron disorder resulting from exon 7 deletion of the SMN1 gene. Neuromuscular ultrasound has been shown to be useful in evaluating neuromuscular disorders including SMA, and is increasingly being used to assist in diagnosis of nerve entrapment through direct visualization of the peripheral nerves as they traverse areas of possible obstruction. In our patient, EMG interpretation was challenging given her underlying neuromuscular disorder. The availability of neuromuscular ultrasound was beneficial in helping to aid in the diagnosis of ulnar nerve entrapment.

Conclusions: Neuromuscular ultrasound is a helpful tool that can aid in the assessment for superimposed focal entrapment neuropathies in patients with neuromuscular conditions when the diagnosis is unclear or not possible on electrodiagnostic testing.