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Hereditary neuropathy with liability to pressure palsies (HNPP) is a focal and recurrent hereditary motor and sensory neuropathy. First symptoms appear rarely before the age of 20 years. This disorder is characterized by acute episodes of weakness and paresthesia arising in a defined territory of a nerve trunk. These attacks, which often occur after minor injury or prolonged nerve compression, often regress but have the tendency to relapse, either in the same or in a different nerve. Paralysis can remain permanent. The electrophysiological manifestations consist of prolonged distal motor latencies and slowed conduction velocities at usual sites of nerve compression. Sausage-shaped swellings of the myelin sheath (tomacula) are characteristically found on nerve biopsy. HNPP is inherited as an autosomal dominant trait. In 80% of cases, the genetic anomaly is a 1.5 Mb deletion in chromosomal region 17p11.2 including the PMP22 gene. The deleted region is identical to the region duplicated in Charcot-Marie-Tooth disease type Ia (CMT1A). The identification of this deletion confirms the diagnosis. Point mutations within the PMP22 gene have been identified in rare HNPP cases. Treatment is symptomatic and is aimed at preventing nerve compression. |