Charcot-Marie-Tooth disease (CMT) is named after the three doctors who first described the disease in 1886: Jean-Martin Charcot (shar-coh), Pierre Marie, and Howard Henry Tooth. Today, CMT refers to any peripheral neuropathy with a genetic cause, whether or not the specific genetic mutation is known.
CMT is a rare multisystem, multiorgan disease that causes lifelong, progressive symptoms, including muscle weakness and atrophy in the arms and legs, sensory loss, and other complications. These symptoms often lead to challenges with balance, walking, hand use, and other daily activities. Early and accurate diagnosis is essential for understanding the type of CMT, guiding treatment decisions, and empowering individuals and families with the tools they need for management and support.
What Are CMT Symptoms?
CMT symptoms vary widely from person to person, but common signs include:
- Muscle weakness, particularly in the lower legs, feet, and hands, can lead to difficulty walking.
- Foot deformities, such as high arches or flat feet, and issues like foot drop (inability to lift the front of the foot) and ankle instability may cause frequent tripping and falling.
- Challenges with balance and coordination, often due to proprioception deficits, which is the reduced ability to sense the position and movement of the body’s limbs in space.
- Loss of sensation or tingling in the feet, legs, hands, or arms.
- In children, early signs may include toe walking, frequent ankle sprains, or trouble with fine motor skills, such as writing or using zippers and buttons.
- Additional symptoms may include chronic pain, fatigue, hip dysplasia, neurogenic bladder, optic atrophy, hearing loss, and for some, breathing difficulty.
These symptoms are often the first signs of CMT and can vary widely in severity and progression. Recognizing them early is essential, as timely evaluation and diagnosis can help individuals access the necessary care and support. Clinic directors at CMTA Centers of Excellence encourage anyone experiencing these symptoms to consult a neurologist for a thorough diagnostic workup and guidance on the next steps.
Why is Early CMT Diagnosis Important?
Early diagnosis of CMT is essential for accessing the needed care and resources. Diagnosing CMT early allows individuals to begin tailored treatments, such as physical therapy, orthotics, and other assistive devices as needed. It also opens the door to participation in clinical trials and opportunities to contribute to advancing research as a CMTA patient partner.
Clinic directors at CMTA Centers of Excellence emphasize that early and accurate diagnosis is key to understanding the specific type of CMT, planning for long-term management, and making informed family planning decisions.
How is CMT Diagnosed?
Diagnosing CMT involves combining multiple tools to create a complete diagnostic picture:
- Clinical evaluation begins with identifying common symptoms, such as muscle weakness, foot deformities, balance challenges, and numbness/tingling sensations, while considering family history for patterns that suggest CMT. Doctors will also try to rule out other potential causes of neuropathy symptoms, such as diabetes or vitamin deficiencies like B12 deficiency, which can mimic CMT symptoms.
- Nerve conduction studies (NCS) measure how quickly and effectively nerves transmit signals. Abnormal nerve conduction is expected in CMT and can help determine the type: very slow conduction indicates a demyelinating CMT (CMT1), and conduction that is not very slow suggests an axonal CMT (CMT2).
- Genetic testing can confirm the diagnosis by identifying the genetic cause and specific subtype. However, it is not always conclusive and must be considered alongside clinical and electrodiagnostic findings.
By combining these tools, doctors can ensure an accurate diagnosis while ruling out other potentially treatable conditions. When genetic confirmation isn’t immediately available, the diagnosis is a clinical diagnosis that’s based on symptoms, family history, and NCS results.
What is a Clinical CMT Diagnosis?
Doctors may clinically diagnose individuals with CMT1 (demyelinating) or CMT2 (axonal) based on symptoms and NCS findings:
- CMT1 (Demyelinating): NCS results show slower nerve conduction velocities (<38 m/s) with relatively uniform findings across tested nerves.
- CMT2 (Axonal): NCS results show faster conduction velocities (>38 m/s), significantly reduced amplitudes, and variable findings between nerves.
Once the responsible genetic mutation is identified, the diagnosis transitions to the subtype associated with that mutation, such as CMT1A, CMTX1 (aka CMT1X, CMTX), or another subtype. Genetic testing provides this confirmation when available.
Can I Have Normal Nerve Conduction Study (NCS) Results and Still Have CMT?
Yes, in some cases, individuals with CMT can have normal NCS results, particularly early on or with certain subtypes like CMT2D. Experts at CMTA Centers of Excellence emphasize the importance of testing multiple nerves in both arms and legs to ensure a comprehensive evaluation.
- CMT1 (Demyelinating): Typically shows uniform abnormalities on NCS and is often detectable even before symptoms develop.
- CMT2 (Axonal): May present variability, with some nerves showing clear abnormalities while others appear normal, depending on the progression.
When CMT is suspected, but NCS results are normal, doctors may consider other conditions like Small Fiber Neuropathy (SFN). SFN shares similar symptoms but does not cause detectable abnormalities on NCS.
Nerve conduction studies are just one part of the diagnostic picture. A thorough evaluation that combines multiple tools helps ensure an accurate diagnosis and a clearer understanding of CMT.
Is Genetic Testing Needed for Diagnosing CMT?
No, genetic testing is not required to diagnose CMT. A clinical diagnosis based on symptoms, nerve conduction study (NCS) results, and family history can determine whether someone has CMT.
Genetic testing, however, is valuable for confirming the diagnosis and identifying the specific subtype of CMT. It’s important to note that genetic testing doesn’t always provide answers. Testing panels may not include all known CMT genes, and some mutations remain undiscovered. A negative genetic test result does not rule out CMT. It simply means the genetic cause was not identified.
Genetic testing complements clinical evaluation and NCS findings to provide a fuller understanding of the diagnostic picture.
Why Is Family History Important in Diagnosing CMT?
CMT often runs in families, so understanding family history is an important part of diagnosis. Doctors look for patterns of symptoms, such as muscle weakness or balance difficulties, that may suggest inherited neuropathy.
However, a lack of family history does not rule out CMT. Sometimes, the diagnosis may remain unclear even with a strong clinical picture, requiring further testing and monitoring.
What Happens If My Diagnosis Is Unclear?
In some cases, a definitive diagnosis may not be immediately possible. This can happen if nerve conduction study (NCS) results are inconclusive or genetic testing does not identify a known mutation. Doctors rely on the overall clinical picture when this occurs and may recommend additional testing or ongoing monitoring.
Specialists at CMTA Centers of Excellence are experienced in managing complex cases and ensuring all potential causes are thoroughly evaluated and addressed.
Where Can I Find a CMT Specialist?
CMTA Centers of Excellence are multi-disciplinary clinics dedicated to diagnosing and caring for individuals with CMT. Staffed by world-renowned physicians, clinicians, and researchers specializing in CMT, these centers provide comprehensive evaluations and expert guidance to confirm or refine a diagnosis.
Visit the CMTA Center of Excellence directory today by clicking the button below to find your nearest and take the next step in your journey.
