Charcot Marie Tooth disease

Charcot-Marie-Tooth disease (CMT) is an inherited condition that affects nerves or myelin, a protective covering around nerves. In individuals born with the defective genes, nerves gradually shrivel up and die, a process called axonal degeneration. As muscles require input from nerves to survive, the death of these nerves causes the secondary degeneration of their associated muscles. This leads to weakness then muscle wasting and deformity, and eventually arthritis. In addition, sensory nerves are often affected, so that numbness is common. Condtions like CMT are called by the general term 'neuromuscular' disorders, which means simply disease affected nerves then muscles.

Although all nerves to muscles are affected, the nerves travelling to your arms and legs are the longest and most likely to degenerate. For this reason, many people first experience symptoms in their feet. This gradually travels up their legs and into their thighs, as well as beginning in their hands and moving up the arms. Different forms of CMT begin at different ages depending on severity, however many appear in adolescence or early adulthood. The types vary widely in severity, even among family members, but tend to slowly worsen over time. It is important to remember that the disease begins long before symptoms are present, so genetic testing is highly recommended for family members.

Charcot-Marie-Tooth disease affects about one person in 2,500 and is the most common inherited neuromuscular disorder. It is usually managed by a rheumatologist, physiotherapist, podiatrist and other specialists.

Different types of Charcot-Marie-Tooth - Classification and Significance

There are many different genes involved in Charcot-Marie-Tooth, however the many different types are broadly grouped into

  • CMT1 – disorders of the protective 'myelin' casing around the nerves

  • CMT2 – the nerve shrivels up ('axonal degeneration')

  • Purely motor CMT (dHMN)

There are, however, sub-types and mixed patterns of CMT that do not fit easily into this division.

CMT1 - Myelin is a special coating on nerves that helps the signals from the brain to travel quickly ('conduction'). De-myelinating diseases, like CMT and the more commonly known MS (multiple sclerosis), have slow nerve conduction, secondary degeneration of the underlying nerve, andabnormal formations of myelin clumps ('onion-bulb formations').The most common form of CMT is the moderately severe CMT1A. The most severe form of CMT also fits into this group and is called Dejerine-Sottas neuropathy, a rapidly worsening form that may involve the eyes in addition to the arms and legs.

CMT2 - The axon is the long string-like section of nerve that travels through the body (as opposed to the 'nerve body' which sits in the spinal cord or brain). Axonal degeneration is a process where the axon breaks down then is regrown, only to break down again. With each regrowth, the axon is progressively more abnormal. In this form of CMT, the speed of nerve conduction is relatively normal.

Differential Diagnosis

Though CMT is usually quite easily identifiable to the doctor, there are a number of other rare conditions that appear similar, including acquired neuropathies, motor neuron diseases and distal myopathies.