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Pyomyositis 121

Rarely, pyomyositis can present with acute fever and chills, also with Late or Septic Stage
toxic shock syndrome or pyrexia of unknown origin. It may present as If the abscess remains untreated, dissemination of infection occurs.
an acute abdomen or spinal compression or compartment syndrome, Bacteraemia, septicaemia, septic shock, multiple organ dysfunction
depending on the anatomic location of the affected muscle. It has been syndrome, and metastatic abscesses are some of the complications.
reported that about 5% of patients present in this stage. 3 Investigations
In children younger than 5 years of age, when the lower limb is affected the
main complaint on presentation may be that of an inability or refusal to walk. Needle Aspiration
9
In the tropics, the abscess is usually solitary, but multiple abscesses may When the diagnosis of pyomyositis is suspected, particularly for
be seen in some patients. The clinical manifestations in both tropical and patients presenting in the suppurative or late stages, the swelling should
nontropical pyomyositis are similar and can be categorised in three stages: be aspirated with a large-bore needle (not smaller than 18 gauge) to
3
invasive, suppurative, and late or septic (Table 19.1). confirm the presence of pus. The aspirated pus is usually yellowish in
colour but may be brownish or blood-stained.
Table 19.1: Clinical stages of pyomyositis.
Microbiology
Clinical stage Features
Any aspirated and/or drained pus should be cultured (aerobic and
Duration of symptoms <10 days anaerobic). A biopsy of the abscess wall and/or muscle taken at time
of open drainage should also be cultured. The culture should help to
Pain in affected muscle identify the bacteria involved in the pathology. Blood should also be
cultured to identify any septicaemic process. A sensitivity test would be
Low-grade fever helpful in the choice of antibiotics, but this should not delay institution
Invasive
Wooden or hard stiffness on palpation of muscle of antibiotic therapy.
Imaging
Mild leucocytosis
Early radiological evaluation is a key to diagnosis of pyomyositis when
Needle aspiration negative for pus a high index of suspicion exists. Ultrasonography should be used first
because it is inexpensive and widely available, without the disadvan-
Duration of symptoms 10–21 days tage of delivering a relatively high radiation dose to children. It has
been shown that early application of sonography to any suspected les-
Oedema son can help to establish early diagnosis of pyomyositis. 16,17
Ultrasound features in the muscle include: 16
Marked tenderness of affected muscle
Suppurative • muscle swelling;
Pyrexia
• hypoechoic areas in the muscle belly;
Leucocytosis • heterogenous hypoechoic areas; and
Needle aspiration yields pus • hyperechoic areas.
Other advanced imaging techniques, such as magnetic resonance
Duration of symptoms >21 days
imaging (MRI), computed tomography (CT) scan, and radionuclide
Fluctuant swelling in muscle scanning, if available, could help in identifying occult muscle abscesses
or multifocal involvement. MRI, due to its excellent soft tissue
High-grade fever resolution properties, is particularly useful, especially in deeply sited
muscles that are not readily accessible to clinical examination. MRI
Late or septic Severely ill
features of pyomyositis include the following. 18
Septicaemia • The affected muscle may appear swollen, with loss of architectural
definition.
Leucocytosis
• Heterogenous areas of low intensity appear on T1-weighted images.
Needle aspiration yields pus
• In the early stage, the only finding may be oedema (area of high
signal intensity on fluid-sensitive sequences).
Invasive Stage It has been noted that MRI with gadolinium enhancement can
The invasive stage is characterised by an insidious onset of dull cramp- increase the confidence of identifying or excluding the presence of
abscess,
but this may give high-dose irradiation to the child.
11,19
ing pain, with or without fever and anorexia. There is localised oedema, Plain radiograph of the affected limb should always be done to
which is indurated or woody but usually causes little or no tenderness exclude acute osteomyelitis, but it should always be remembered that,
and lasts for about a week. Only about 2% of all patients (both adults in the early stages, x-ray may not diagnose osteomyelitis. Clinical
and children) present in this stage. 3
suggestion of complication by pneumonia, pleural effusion, and
Suppurative Stage pyopericardium should warrant that a chest radiograph may need to be
The suppurative stage occurs when a deep collection of pus has devel- done serially. If the latter complication is suspected, an echocardiogram
oped in the muscle, usually from the second to the third week of the would be helpful.
infection. The patient may complain of fever with chills. The overlying Haematological Tests
skin is mildly erythematous, and the swelling is fluctuant. Leucocytosis
A complete blood count should be done. Leucocytosis, neutro-
may be present, with elevated erythrocyte sedimentation rate (ESR) or
philia, or eosinophilia may be present, and patients presenting late
C-reactive protein (CRP). A needle aspiration test is usually productive
are often anaemic.
of pus. A little more than 90% of patients seen in sub-Saharan Africa
3
would typically present in this stage.