MDA Support

MDA clinics offer an interdisciplinary team approach toward initial diagnosis and follow-up care. Individuals suspected by their physicians of having neuromuscular disorders included in MDA’s program have access to a nationwide network of MDA clinics staffed by neuromuscular disease specialists. The MDA clinic physician can advise about the initial diagnosis and recommend measures to medically manage neuromuscular disease. MDA clinic follow-up care ranges from management of symptoms to medical intervention designed to assist individuals in maintaining the highest possible quality of life.

To locate the MDA clinic in your area, go to www.mda.org, or call (800) 572-1717.

Diagnosis: What's Involved

MDA support groups provide an opportunity to share information.

The first step in medical care is determining the nature of the disease. The MDA clinic team can perform diagnostic examinations and recommend pertinent laboratory tests. Some of these tests may be extensive, yet in most instances they can be done on an outpatient basis. Information about genetic-based diagnostic testing is available at the MDA clinic.

Following clinical examination and analysis of the laboratory tests, many neuromuscular diseases can be quickly and accurately diagnosed. Some neuromuscular diseases, however, can be more difficult to diagnose. In these cases, the physician will make what is called a differential diagnosis listing two or more diseases that have similar symptoms. A definitive diagnosis may require waiting until the disease has progressed to a stage that is unique to that disease.

With the majority of neuromuscular diseases, the first noticeable symptom is usually a persistent weakness in one or more muscles.

Muscles can become weak for many reasons. The first question the physician will seek to answer in trying to establish a diagnosis is whether muscle function is abnormal because there is a disease of muscle itself, or whether muscle function is abnormal because of a disorder that has developed in other tissue (e.g., nerve). The following two pages describe the most common diagnostic and laboratory procedures used to determine why muscle function is abnormal and arrive at a definitive diagnosis.

Diagnostic Procedures

Clinical examination

The clinical examination of someone suspected of having a neuromuscular disease focuses on muscle strength. Muscles are examined with special attention given to those of the arms, legs, shoulders and hips. A few neuromuscular diseases affect facial muscles, and these too are examined.

Determining which muscles are not weak is as important as determining which muscles are weak. Each neuromuscular disease typically shows a specific pattern of muscle involvement. A final diagnosis is based in large part on the pattern of muscle involvement detected during the clinical examination.

Family history

Many neuromuscular diseases — including all of the muscular dystrophies — are genetic diseases. Knowledge of other cases in the family can help to establish and/or confirm a diagnosis.

Nerve conduction and electromyogram

These two tests are often performed at the same evaluation. The nerve conduction studies measure the ability of nerves to conduct impulses to muscle; this is an important test when evaluating for disorders such as Charcot-Marie-Tooth disease. An electromyogram (EMG) measures electrical activity of muscle. Diseased muscle has an electrical activity characteristically different from that of normal muscle.

Serum enzyme tests

Serum enzyme tests measure the amount of muscle proteins present in the blood. Where muscle tissue is healthy, these proteins remain in muscle and the amount present in blood is relatively low.

Many, but not all, neuromuscular diseases that cause muscle destruction lead to a significant increase in the muscle protein levels found in the blood. Thus, serum enzyme tests can be important aids in the diagnosis of neuromuscular diseases.

The value of these tests is greatest at the early stages of the disease. At the earliest disease stage, muscle mass is relatively great, and changes in serum protein levels may occur even before symptoms such as weakness become apparent.

At later disease stages, however, muscle mass may be so reduced that serum protein levels may even appear normal.

• Creatine kinase (CK): This protein is confined almost exclusively to muscle, and a higher than normal CK level in blood serum indicates a leakage from muscle tissue. Determination of the serum CK level is an important laboratory test in the diagnosis of Duchenne muscular dystrophy and other muscle diseases.
  
  
• Other enzymes: Increased levels in blood serum of aldolase, lactic dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), pyruvate kinase (PK), and several other enzymes also may be diagnostically significant.

Genetic tests

A small amount of blood can be used to extract DNA from blood cells. This is extremely valuable for diagnosing genetic defects which can cause specific neuromuscular diseases. One of the strengths of these tests is that they reveal the same abnormality regardless of the stage of the disease.

Muscle biopsy

The muscle tissue is surgically removed (a muscle biopsy) for microscopic and/or biochemical analysis. For some neuromuscular diseases, a final diagnosis depends on the analysis of a muscle biopsy. The amount of muscle removed is roughly equivalent in size to the tip of a little finger. In some conditions, such as the inflammatory myopathies and central core disease, the muscle tissue has a characteristic appearance under the microscope.

The muscle tissue can be analyzed for abnormalities in a number of proteins within muscle cells. For example, dystrophin is absent or greatly diminished in the muscle cells of those with Duchenne muscular dystrophy. It is present in an abnormally low amount or altered form in the muscle cells of those with Becker muscular dystrophy. Similarly, other muscle proteins may be missing in different types of muscular dystrophy.