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Facioscapulohumeral Muscular Dystrophy (FSH, FSHD)

Diagnosis

A diagnosis of facioscapulohumeral muscular dystrophy (FSHD) is suspected in patients who present with weakness of the face, shoulder girdle, and upper arm(s) with relative sparing of the deltoid muscles. Patients with suspected muscular dystrophy should be referred to a specialist with expertise in neuromuscular disorders (where available) for evaluation and diagnosis.

Today, the most reliable way to diagnose FSHD is with a test for a tiny missing section of DNA on chromosome 4. A commercial genetic test for FSHD detects shortening of the repeated DNA elements (D4Z4) located within the 4q35 region of chromosome 4. This diagnostic test, performed on blood cells, is positive in approximately 95% of typical FSHD cases. The test is considered highly accurate for FSHD.

Genetic testing is not needed for every affected person with a typical clinical presentation if the family history is consistent with autosomal dominant inheritance and the diagnosis has been genetically confirmed in a first-degree relative.1 (See Causes/Inheritance.) In many cases, however, people with no family history are suspected of having either FSHD or some other neuromuscular disorder. In these situations, less expensive and less specific tests than the FSHD DNA test may be done first.

One test is a creatine kinase level. This test, also performed on a blood sample, measures the amount of an enzyme known as creatine kinase in the blood. When muscle cells break down, as they do in muscular dystrophies and some other disorders, the creatine kinase, or CK, level is elevated. CK is often elevated up to 5 times the upper limit of normal in symptomatic FSHD patients. CK is rarely elevated in patients with no symptoms.

Another type of diagnostic test is the electromyogram, or EMG, which measures the electrical activity in the muscles, displayed in the form of waves. EMG typically displays alterations in patients with FSHD.

Another diagnostic procedure sometimes undertaken is a muscle biopsy. In this procedure, a small piece of muscle is taken, under local anesthesia, usually from the arm or leg. Biopsy samples reveal cellular and molecular abnormalities that suggest certain muscle disorders and rule out others.

Muscle biopsies are less often performed today than in the past, especially when there is a DNA test for the disease a doctor suspects is causing the symptoms — as there is for FSHD. Neither EMG nor muscle biopsy are needed when the diagnosis of FSHD is confirmed by genetic testing.

Confusion with other disorders

FSHD can be confused with polymyositis, which is neither a genetic disease nor a muscular dystrophy. It also can be confused with certain conditions of the nervous system that are not muscle disorders.

Seeing a neurologist who specializes in neuromuscular disorders at an MDA Care Center or major medical center will increase the possibility of an accurate diagnosis.

Diagnoses made many years ago (for example, in older family members) may be worth revisiting because new gene panels and different types of genetic testing have been developed since the 1990s. For more on getting a definitive genetic diagnosis, see The Genie's Out of the Bottle: Genetic testing in the 21st century

References

  1. Tawil, R. et al. Evidence-based guideline summary: Evaluation, diagnosis, and management of facioscapulohumeral muscular dystrophy. Neurology (2015). doi:10.1212/WNL.0000000000001783

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