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Clinical Characteristics

The majority of patients complain of muscle and sometimes joint pain for a few days before any swelling develops. The pain may make movement difficult. Many have mild malaise and a low pyrexia, but there are no other consistent symptoms and, in contrast, some patients are afebrile and free of systemic complaints. In a few patients the onset is acute, with high fever: this usually occurs with the less common streptococcal infections. Almost all patients have local swelling, with a hot shiny skin over the infected area. In about one-third to one-half there will be local fluctuation, but in others there is no pus and the clinical emphasis is on the pain, swelling, and immobility. As the abscess develops, the muscles become hard, tense, and more swollen. The majority of patients (70%-80%) will have one abscess; the remainder either have no localized abscess or multiple abscesses when first seen. The thigh is the most common site (Fig. 30.1). There is regional lymphadenopathy in less than one-third of the patients.

The distribution of the lesions was very well described in several of the earlier reports (e.g., Sayers 1930 and Robin 1961; Fig. 30.3). The pattern does not appear to have changed in recent series, and the more frequent use of ultrasound is localizing the sites more accurately.

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Fig. 30.3. A The site of lesions in 12 patients with tropical myositis in Malaya (Courtesy of Dr. G. C. Robin and J Trop Med Hyg, 1961) B The site of pyomyositis in 26 patients in the Solomon Islands. C The distribution of pyomyositis in the abdominal muscles of five patients in the Solomon Islands. (B, C courtesy of Dr. E. G. Sayers and Trans R Soc Trop Med Hyg, 1930).

There is a hyperacute version, which can be rapidly fatal. At any stage there can be septic shock. The abscess in one elderly man was so large that the brachial artery was compressed and the forearm was gangrenous. This patient died, as did a 10 year-old girl who was in shock when admitted to hospital. Other complications have included multiple metastatic abscesses in the brain, lungs, liver, kidney, vertebrae, and heart. Abscesses have ruptured into the chest or abdominal cavity and either of these complications may be fatal. The overall mortality may be as high as 1% or 2%.

Although many therapeutic regimens have been described, antibiotic therapy alone is usually disappointing. Surgery is almost always required; ultrasound-guided needle aspiration will accurately localate any small amount of pus. Without such guidance, needle aspiration may be unsuccessful and therefore misleading; sometimes this is because the pus is thick and difficult to aspirate. Pus may develop in as short a period as 24 hours, but incision before pus has collected seems to do no harm (except perhaps to the doctor's ego?). In the early stages there may be clusters of small ragged abscesses, but these tend to coalesce rapidly and spread within the muscle. After the pus is removed, there is very little hemorrhage in most patients. The surrounding muscle is usually very pale and "gelatinous." Healing is usually complete in half of the patients within 2 weeks. Persistent swelling or lack of improvement in the patient's general condition are indications for an ultrasound survey to exclude unsuspected pus, not only locally, but elsewhere, e.g., the liver. A chest x-ray is also required, and may be advisable even before surgery and again as clinically indicated. Lung abscesses can be clinically silent.

Cardiac complications have occurred in several series, for example, from Uganda and Nigeria: all are probably the result of bacteremia. A positive blood culture can be obtained in up to 10% of cases, but it has also been suggested that pyomyositis is a widespread disorder of skeletal and cardiac muscles. Cardiac complications are more common in patients who have multiple abscesses: the bacteremia responds to antibiotics in most patients, but septic pericarditis may cause tamponade and sometimes requires drainage. When constrictive pericarditis ensues, surgical pericardiectomy may be required. This can be hazardous, because adhesions are common when there has been severe septic pericarditis. Other cardiac complications have included acute S. aureus endocarditis, microabscesses in the myocardium (as well as the liver, spleen, and kidneys), diffuse acute myocarditis, arrhythmias, and valve infection. Anterior uveitis also occurred in one patient.

If the patient survives and the muscle abscess is drained satisfactorily there may be little residual disability, but the necrotic muscles do not regenerate and local wasting and deformity persist. When the patient is a child, tropical pyomyositis may interfere with the normal development of adjacent bones. In the majority, however, considering the severity of the illness, there is remarkably little residual disability.

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