34 years old male with fever, cough, and knee pain

History
34 years old male with fever, cough, and painful left knee since returning from a Thailand visit 2 weeks before presentation. He complaints about night sweats and weight loss of 5 kg.

Findings
Conventional chest X-ray shows enlargement of left pulmonary hilum compatible with adenopathy (A). In the thoracic CT scan in soft tissue window (B) and lung window (C) there is evidence of lobar consolidation in left anterior upper lobe including an area with fluid density and intralesional gas. The MRI of left knee (D; left: T2-weighting with fat saturation; right: post contrast T1-weighting with fat saturation) shows joint effusion, hyperenhancement of thickened synovialis, and bone marrow edema with irregular contrast enhancement in medial femoral condyle.

Diagnosis
Lobar pneumonia with lung abscess formation and septic arthritis of left knee with osteomyelitis in left femur. Evidence of Burkholderia pseudomallei in blood culture.

Discussion
The Gram-negative aerobic bacillus Burkholderia pseudomallei is the causative agent of an infectious disease called melioidosis (a.k.a. Whitmore`s disease, Pseudo-Rotz). The bacterium is an environmental saprophyte found in wet soils predominantly in southeast Asia and northern Australia. Melioidosis is the third most common cause of death from infectious disease in northeast Thailand, exceeded only by HIV infection and tuberculosis. Burkholderia pseudomallei is spread to humans either through inhalation of contaminated dust or by direct contact between abraded skin and contaminated soil. It mostly infects adults with predisposing conditions, such as diabetes mellitus, chronic renal failure, hematological disorders, and connective tissue disorders, especially those on immunosuppressive therapies. In other words, since up to 80% of patients with melioidosis have one or more risk factors for the disease, it has been suggested that melioidosis should be considered an opportunistic infection that is unlikely to have a fatal outcome in a previously healthy person.

Melioidosis presents as a febrile disease, ranging from fulminant septic illness to chronic infection that may mimic cancer or tuberculosis. The disease is characterised by abscess formation. Any organ system may be potentially affected. Lung, liver, spleen, skeletal muscle, and bones and joints are the most commonly affected sites with the lung as the most frequently involved organ.

The radiological findings in patients with acute pulmonary melioidosis include multiple small pulmonary nodules due to hematogenous spread and lobar infiltrations that start in the upper lobes and which may result in cavity or abscess formation. Generally, there are no radiological features specific to pulmonary melioidosis. The radiological findings resemble those commonly seen for community-acquired pneumonia and tuberculosis. However, in melioidosis, simultaneous involvement of other organs is common. Pleural involvement, such as effusion or empyema, and mediastinal or hilar adenopathy are considered to occur only rarely in melioidosis.

In the musculoskeletal system the joints are the most commonly affected sites, usually occurring via the hematogenous route. Radiological features, which are best depicted on MRI, include effusion, synovial enhancement, periarticular osteomyelitis, and overlying muscle edema or microabscesses.

Treatment of melioidosis consists of an intensive phase of at least 10 to 14 days of ceftazidime, meropenem, or imipenem administered intravenously, followed by oral eradication therapy, usually with trimethoprim–sulfamethoxazole (TMP-SMX) for 3 to 6 months.

Recommended reading

Wiersinga et al.
Melioidosis
N Engl J Med (2012) 367:1035

Kim et al.
Radiological manifestations of melioidosis
Clinical Radiology (2010) 65:66

Muttarak et al.
Spectrum of imaging findings in melioidosis
BJR (2009) 82:514

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