Chronically Tardy: Hereditary Liability to Pressure Palsy Presenting with Ulnar Neuropathy at the Elbow

Figure 40-1 Right ulnar motor inching study across the elbow region recording from the abductor digiti minimi muscle. Stimulation sites of successive potentials (from top to bottom) are listed in relationship to the medial epicondyle of the humerus: potential 1 is 7.5 cm distal; potential 2 is 4.2 cm distal; potential 3 is 1.4 cm distal; potential 4 is 3 cm proximal; and potential 5 is 6.2 cm proximal. The major drop in amplitude occurs between potentials 2 and 3, indicating that the site of conduction block is located between the points 4.2 and 1.4 cm proximal to the medial epicondyle. The stimulus artifact is seen on the far left of traces 1, 2, and 5.

This patient’s electrophysiologic studies were typical of multiple compression neuropathies, with focal conduction abnormalities in the median nerves localized to the wrist and in the ulnar nerves localized to the elbow region. However, the patient’s clinical history of recurrent episodes of nerve dysfunction with spontaneous recovery beginning in the teen years was most unusual for compression mononeuropathies and highly suggestive of HNPP. A DNA study, performed on whole blood by Athena Diagnostics, showed a deletion in the 17p11.2 gene, confirming the clinical suspicion of HNPP.

The patient was counseled on the hereditary nature of this neuropathy and that his intermittent episodes of ulnar nerve dysfunction were related to HNPP. Genetic testing was declined by his mother and two siblings. The fact that the needle examination did not show fibrillation potentials in a distal ulnar-innervated muscle despite many years of episodic nerve dysfunction provided a strong argument that the nerve pathology was purely demyelinating. Likewise, the history of spontaneous recovery and absence of evidence of axonal loss provided compelling arguments against considering surgical decompression of the ulnar nerve at the elbow region. The patient was advised to avoid sustained or repetitive elbow flexion and to avoid direct compression on the elbow region to reduce the risk of nerve dysfunction secondary to superimposed ulnar nerve compression injury.

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