Sonographic Evaluation of the Peripheral Nerves in Hereditary Neuropathy With Liability to Pressure Palsies: A Case Report
A 73-year-old, right-handed woman visited our hospital in September 2010, complaining of right foot drop and numbness on right lower leg in the previous month. There was no history of diabetes, trauma or any other polyneuropathy. She had undergone a lumbar disc operation five years previously. In particular her first son and grandson had a history of transient monoparesis of upper limbs that spontaneously resolved.\nNeurological examination revealed weakness of right foot dorsiflexion and eversion (Medical Research Council scale grade 3) and reduced pinprick and touch sensations on the dorsal side of the right foot and the lateral aspect of the lower leg. Deep tendon reflexes at both knees and ankles were decreased.\nElectrodiagnostic studies showed a right peroneal neuropathy around the knee level and chronic bilateral L5 radiculopathy. The sonographic examinations demonstrated swelling of right common peroneal nerve around the fibular head level (cross-sectional area [CSA], 18 mm2), compared with contralateral side (CSA, 9.6 mm2).\nSix months later, while she was recovering from foot drop, she had another presentation with wrist drop on the right side. Electrodiagnostic studies were performed to rule out radial neuropathy. Motor nerve conduction studies showed prolonged distal latency and reduced compound muscle action potential amplitude in the right median nerve and no response in the right peroneal nerve. The ulnar nerve's segmental conduction velocities across the elbow were decreased (). In sensory nerve conduction studies, sensory nerve action potentials (SNAP) of both median nerves and right superficial peroneal nerve were not generated. The distal sensory latency was prolonged, and SNAP amplitude was reduced in both ulnar nerves (). In needle electromyography, ulnar innervated muscles including the abductor digiti minimi, first dorsal interosseous, and flexor carpi ulnaris showed large amplitude, long duration and polyphasic motor unit action potentials (MUAP) with reduced recruitment. In the forearm muscles innervated by radial nerve, extensor digitorum communis and extensor indicis proprius showed no MUAP. However brachioradialis and extensor carpi radialis longus muscles did not show any abnormalities. Median innervated muscles, such as abductor pollicis brevis and flexor carpi radialis, showed long duration and polyphasic MUAP. In lower limb muscles, abnormal spontaneous activities and large amplitude, long duration and polyphasic MUAP with reduced recruitment were demonstrated in right peroneal innervated muscles, such as tibialis anterior and peroneus longus (). These electrodiagnostic studies suggested not only right radial neuropathy, but also bilateral median, ulnar neuropath and right common peroneal neuropathy. The clinical findings and electrodiagnostic findings suggested HNPP, and the diagnosis was confirmed by genetic test demonstrating a PMP22 gene deletion.\nPeripheral nerves of the upper and lower extremities were examined by ultrasonography with an HD15 ultrasound system (Philips Ultrasound Inc., Bothell, WA, USA) using a 7-12 MHz linear array transducer. We traced most of the peripheral nerves, which were typically measured in previous studies about normal reference values of CSA in sonography, including median nerve at the level of carpal tunnel inlet and outlet in the forearm at the antecubital fossa and mid-humerus, ulnar nerve at the wrist and elbow, mid-humerus and radial nerve in the forearm and spiral groove level, common peroneal nerve at the fibular head level, tibial nerve at the popliteal fossa, sciatic nerve in the distal thigh and cervical roots at the C5-8 level. All measurements were done on the right side. CSA was measured using a direct tracing method just inside the hyperechoic rim of each nerve, and the CSA findings were compared with normal reference values [-].\nThe CSA of the median nerve at the carpal tunnel inlet and outlet (CSA, 10.8 mm2 and 9.8 mm2; normal value <6.7 mm2) and in the forearm (CSA, 12.7 mm2; normal value <10.7 mm2) was enlarged (). However the CSA of median nerve at the antecubital fossa (CSA, 13.1 mm2; normal value <13.2 mm2) and mid-humerus level (CSA, 10.9 mm2; normal value <13.1 mm2) was not swollen. The CSA of ulnar nerve was enlarged at the elbow (CSA, 9.3 mm2; normal value <8.3 mm2), but not in the wrist (CSA, 4.6 mm2; normal value <8.1 mm2), and not in the mid-humerus level (CSA, 5.0 mm2; normal value <7.9 mm2). The radial nerve was not swollen in the forearm (CSA, 5.5 mm2; normal value <14.3 mm2) or at the spiral groove level (CSA, 5.1 mm2; normal value <13.3 mm2). In the lower limb, the CSA of common peroneal nerve at the fibular head level was enlarged (CSA, 16.2 mm2; normal value <12.1 mm2) (). However, other nerves of lower extremity were not swollen: the tibial nerve at the popliteal fossa (CSA, 23.5 mm2; normal value <55.9 mm2) and the sciatic nerve in the distal thigh (CSA, 49.9 mm2; normal value <80.6 mm2). The cervical nerve roots (C5-8) were not enlarged at any root level: C5 root (CSA, 6.8 mm2; normal value <7.8 mm2), C6 root (CSA, 10.3 mm2; normal value <12 mm2), C7 root (CSA, 11.6 mm2; normal value <14.2 mm2) and C8 root (CSA, 9.8 mm2; normal value <14.4 mm2) ().