Several definitions exist for the term “intermediate”. The existence of the latter is a controversial topic. the demyelinating type (CMT1) defined by a motor conduction velocity (MCV) of the median or ulnar nerve of less than 38 m/s, the axonal type (CMT2) with MCV above 38 m/s, and an intermediate type.

Based on neurophysiologic findings three different subtypes are distinguished, i.e. Classification is based on a combination of neurophysiologic characteristics, inheritance pattern, and underlying genetic cause.

Despite the genetic heterogeneity, the clinical phenotype is relatively homogeneous. More than 45 causative genes have been identified. CMT is the commonest inherited neuromuscular disorder. The disease was first described in 1886 by Charcot and Marie in France and independently by Tooth in Great Britain and was named after them. DefinitionĬharcot-Marie-Tooth disease (CMT), also known as Hereditary Motor and Sensory Neuropathy (HMSN), encompasses a clinically and genetically heterogeneous group of disorders characterized by predominantly distal muscle weakness and atrophy, and sensory loss. Synonyms: Hereditary Motor and Sensory Neuropathy type Ia (HMSN Ia). Life expectancy is normal.Ĭharcot-Marie-Tooth disease type 1A (CMT1A). Adult CMT1A patients show slow clinical progression of disease, which seems to reflect a process of normal ageing. Treatment is currently symptomatic and may include management by a rehabilitation physician, physiotherapist, occupational therapist and orthopaedic surgeon. Prenatal testing is possible requests for prenatal testing are not common. Offspring of patients have a chance of 50% to inherit the mutation from their affected parent. The mode of inheritance is autosomal dominant and de novo mutations occur. Differential diagnosis includes other inherited neuropathies, and acquired polyneuropathies. Diagnosis is confirmed by finding respectively a PMP22 duplication, deletion or point mutation. Electrophysiological evaluation is needed to determine whether the polyneuropathy is demyelinating. HNPP typically leads to episodic, painless, recurrent, focal motor and sensory peripheral neuropathy, preceded by minor compression on the affected nerve. Distal symmetrical muscle weakness and wasting and sensory loss is present, legs more frequently and more severely affected than arms.

CMT1A usually presents in the first two decades with difficulty walking or running. The prevalence of HNPP is not well known. Overall prevalence of CMT is usually reported as 1:2,500, epidemiological studies show that 20-64% of CMT patients carry the PMP22 duplication. PMP22 related neuropathies comprise (1) PMP22 duplications leading to Charcot-Marie-Tooth disease type 1A (CMT1A), (2) PMP22 deletions, leading to Hereditary Neuropathy with liability to Pressure Palsies (HNPP), and (3) PMP22 point mutations, causing both phenotypes.

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