Diagnosing Muscular Diseases or Myopathies
Family history. This is used to find out the type of transmission (autosomal recessive, autosomal dominant, or X-linked form), taking into account the existence of sporadic mutations.
In addition to the family history, it is important to understand the timing and progression of the disease (acute, sub-acute, or chronic progression), which muscles are affected, the relationship with exercise and the involvement of other organs such as the skin, eyes, heart, lungs, joints and central nervous system. It is also necessary to ascertain the possible consumption of illegal drugs and the habitual medication that the patient takes, especially statins or other drugs that are potentially toxic to the muscles, those that may produce direct toxicity, cause alterations in the immune system, or act as a trigger for a previously undetected muscular disease.
Physical exam. The aim of this is to look for the main muscular signs, but also to examine the other organs, since some of these may play a significant role in the disease.
Tests to diagnose Muscular Diseases or Myopathies
If, after assessing the patient's medical history, as well as that of their family, and performing the physical exam, it is suspected that there is a myopathy present, either acquired or hereditary, certain complementary tests can be performed, such as:
Study of muscle enzymes in the blood (CK, LDH and aldolase). These are enzymes that are mainly found in skeletal muscles and the heart, and in smaller amounts in the brain. If there are high values of muscle enzymes, it is advisable to rule out probable sporadic causes of these alterations; for example, if the patient has done intense physical exercise, has suffered trauma, has been given a vaccine, and so on, in the preceding days. In any case, it is always prudent to repeat the tests after 2-3 weeks to corroborate the analysis.
Electromyogram. This is a test used to study the functioning of the nerves (peripheral nervous system) and muscles. The test essentially consists of recording, by means of special electrodes, the electrical currents that are formed in the nerves and muscles. It also makes it possible to study the neuromuscular junction. The electromyography is a safe, useful and simple test to perform, although it is a little uncomfortable.
MRI. This is a useful imaging test for assessing all the muscles of the body, in the case of total body resonance, or the muscles of the shoulders and hips when limited to those muscle groups. It allows the presence of inflammation and muscular atrophy to be assessed. It also makes it possible to guide the muscle biopsy and assess a characteristic involvement pattern in the context of some myopathies. In some situations, it can even be used to help assess treatment response. The test is not painful and does not involve radiation, unlike a CT scan. Its disadvantage is that it takes a long time, sometimes an hour or more, and some people experience claustrophobia.
Ischaemic Forearm Test. This test evaluates how capable the muscle is of getting energy from glucose. A venous catheter is placed in the forearm and the patient is asked to exercise (squeeze a ball with the hand) in an ischaemic situation (with a pressure cuff). Then the lactate and ammonium levels are compared to the basal levels.
Muscle and nerve biopsy. This is an invasive, but simple procedure that is performed in 20-30 minutes. The test is used to confirm the diagnosis of certain diseases, or to guide the diagnosis which is later confirmed through a genetic study. In most cases where vasculitis is suspected, a nerve and muscle biopsy can be diagnostic.
Genetic study. In some cases this kind of study constitutes the first diagnostic link, for example, when there is clinical suspicion of Duchenne dystrophy, Steinert dystrophy, or facioscapulohumeral dystrophy, for example. On the other hand, in certain myopathies, genetic studies are the last to be carried out, once other diseases have been ruled out by means of muscular resonance and/or muscle biopsy.
Substantiated information by:
Published: 18 November 2020
Updated: 18 November 2020
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