Congenital Muscular Dystrophy (CMD)

Diagnosis

Diagnosing congenital muscular dystrophy (CMD) has become more precise in recent years. In the past, “CMD” was sometimes used as a broad term for early-onset muscle weakness. Today, advances in genetic testing allow doctors to identify specific subtypes based on their underlying cause.

In some cases, people who were diagnosed years ago may benefit from updated testing to clarify their exact condition.

What tests are used to diagnose CMD?

Diagnosis usually begins with a detailed medical history and physical exam. Doctors look at patterns of muscle weakness, muscle tone, and early development to help guide next steps.

To better understand the cause of weakness, doctors may use:

• Blood tests (CK level):
  A creatine kinase (CK) test measures an enzyme that leaks into the blood when muscle is damaged. Elevated CK levels suggest a muscle disorder but do not identify the exact type.
• Genetic testing:
  Genetic (DNA) testing is now the primary tool for diagnosing CMD. A blood or saliva sample is analyzed to identify specific gene changes. This can confirm the diagnosis, define the subtype, and help guide care and family planning.
• Muscle biopsy (less common today):
  In some cases, a small sample of muscle may be examined to look at muscle structure and protein levels under a microscope. With advances in genetic testing, biopsies are used less often than in the past. However, if genetic testing does not provide a definitive answer, a muscle biopsy may help better understand the patient's symptoms and support the diagnosis.
• Electromyography (EMG) and nerve conduction studies:
  These tests may be used to determine whether weakness is caused by a muscle problem or a nerve disorder.
• Imaging and other evaluations:
  Muscle MRI or additional tests may be used in certain cases to better understand the pattern of muscle involvement.

Why genetic diagnosis matters

Identifying the specific type of CMD can:

• Help predict how the condition may progress
• Guide medical care and monitoring
• Determine eligibility for clinical trials or emerging therapies
• Provide important information for family planning

Families who have questions about testing or results may benefit from speaking with a neuromuscular specialist or genetic counselor.

For more on genetic patterns in CMD, see Causes/Inheritance.

Additional reading

• Bönnemann CG et al. Members of International Standard of Care Committee for Congenital Muscular Dystrophies. Diagnostic approach to the congenital muscular dystrophies. Neuromuscul Disord. 2014 Apr;24(4):289-311. doi: 10.1016/j.nmd.2013.12.011.

Last reviewed June 2026.