It Takes a Clinic to Tackle Charcot Marie Tooth Disease
Date: November 30, 2009
It may have an unusual name, but Charcot-Marie-Tooth (CMT) disease is the most common inherited neurological disorder, affecting one out of every 2,500 people. So Johns Hopkins recently established a clinic that specializes in the care of patients with CMT.
Neurologists begin by determining whether the patient does, in fact, have CMT—or another disorder that shares some of the same symptoms. At least half of the patients neurologist Ahmet Hoke sees at the CMT clinic have been misdiagnosed, he says.
Patients with CMT typically present with muscle weakness in the feet, which can later progress to the legs, hands and forearms, and be accompanied by a loss of sensation. A signature of CMT is foot drop, which results from weakened dorsiflexors, and a high-stepped gait. The disease, which is named for the three French doctors who identified it in 1886, results from mutations in the genes that code for proteins found in peripheral nerve axons or their myelin sheaths. Defects in these proteins cause peripheral nerves to degenerate gradually, with subsequent weakening and atrophy of associated muscles.
But not every patient with such symptoms has CMT, says Hoke. Some patients, for instance, are referred with foot deformities that resemble those that can occur in CMT, but the underlying cause turns out to be an orthopedic abnormality. Many other patients are referred with an initial diagnosis of CMT but turn out to have a different form of peripheral neuropathy.
Clinic physicians—Hoke, David Cornblath, Charlotte Sumner and Thomas Lloyd—diagnose CMT through physical exam, family history and nerve conduction studies. Finally, genetic tests can reveal which mutation underlies a patient’s disease. “There’s been a big explosion in the field of the genetics of CMT, especially in the last five or six years,” notes Hoke. “Genetic testing is useful to help predict the prognosis for patients (since different types of CMT progress differently) and helps us in counseling the family about their chances of passing the disease genes to their children.”
For patients diagnosed with CMT, the clinic provides a range of specialty services, including physical therapy, occupational therapy and orthotic specialists. Many patients are fitted for special splints called ankle-foot orthoses that can stabilize gait and prevent patients from tripping and falling. Attentive foot care can help patients reduce the chances of developing ulcers and Charcot joints, potentially painful deformations of the foot and ankle joints.
The Johns Hopkins CMT clinic is one of five centers participating in the North American CMT Registry funded by the CMT Association and Muscular Dystrophy Association. The aim of this registry is to document the natural history of uncommon forms of CMT and identify new genes in CMT patients with no known genetic defects.
The clinic is also participating in a three-site clinical trial to test whether high-dose vitamin C can prevent some nerve degeneration in patients with one genetic subtype of CMT. The results of the study, which is no longer enrolling patients, are expected in February 2011.
CMT may not yet have a cure, says Hoke, but small changes can help patients significantly improve their quality of life
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