Pyomyositis is a bacterial infection of the skeletal muscles, which are attached directly to the bones in the human body. It is usually caused by the bacteria Staphylococcus aureus, the same bacteria that causes pneumonia and toxic shock syndrome. Most incidences of pyomyositis occur in tropical areas of the world; however, it is becoming more common in temperate areas. Despite evidence of the disease spreading, it is still fairly uncommon.
In tropical areas, healthy people between the ages of 10 and 30 years old are most likely to get pyomyositis. In more temperate climates, it tends to appear only in people who have compromised immune systems, for example people who are HIV positive. Even in people fitting this description, the disease is rare because skeletal muscle tends to have a high resistance to all types of infection.
Most people have at least some Staphylococcus aureus in their bodies at some point in their lives. Presence of the bacteria does not necessarily mean the person will get sick. Most people only get pyomyositis if they suffer some sort of muscle trauma during a time when the Staphylococcus aureus is present in their bodies. Damage to the muscle causes the immune system to weaken, allowing the infection a place to take root.
Aside from the obvious issues of suppressed immune system, HIV patients are more susceptible to pyomyositis for other reasons. HIV patients tend to have more Staphylococcus aureus in their bodies than healthy people do. Also, the damage to bone marrow caused by HIV can make the body less able to resist the infection.
Pyomyositis causes several symptoms, both in the infected muscle and in the body as a whole. The disease starts with a low-grade fever and pain in the infected muscle. As the disease progresses, the sufferer may feel severe pain in the muscle. Pus may be present in the infected area. If the disease is allowed to progress, the affected person could die.
Doctors diagnose pyomyositis using an MRI test. Since the disease is so rare, doctors will only test for it if the symptoms very clearly point to it as the culprit or if other possibilities have already been tested for. It is fairly easy to treat pyomyositis if it is caught before it becomes life threatening. Many patients respond to antibiotics. If there is pus in the muscle, the pus may need to be drained to alleviate pressure and pain.