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Q1: What is the diagnosis?
Q2: What is the most appropriate therapy for this patient?
Nocarida was first described by the French veterinarian Edmund Nocard in 1888. Nocardia is a genus in the family nocardiaceae, and there are nine species recognised. Nocardia asteroides is the cause of 80%–90% of all cases of nocardiosis.1 The organism is characteristically a beaded, Gram positive bacillus, which is weakly acid fast. Definitive diagnosis of nocardiosis requires identification of the organism in culture, as the histological appearance of the organism is not unique. Nocardia will grow in a variety of culture media but is slow growing. It is typically identified after 4–5 days but may take up to four weeks to be isolated.1,2
Historically, nocardia were believed to be fungi that only rarely caused disease in humans; however it has now been established that these bacteria may be relatively common pathogens and cause a variety of clinical problems in humans. The main host defence against nocardia is a cell mediated immune response, hence, patients with HIV, lymphoreticular malignancies, and solid organ transplants are at increased risk for developing nocardiosis. Other predisposing conditions include chronic lung disease, systemic lupus erythematosis, tuberculosis, diabetes mellitus, Cushing’s syndrome, or alveolar proteinosis.3 Steroids add significantly to the risk for developing nocardiosis and have been associated with up to 20% of all cases. Interestingly, 50% of cases of nocardiosis occur in patients with no underlying disease or immunosuppressive therapy.
The clinical manifestations of nocardiosis are diverse and patients may present with non-specific systemic symptoms, including anorexia, weight loss, and high fevers. Thus, nocardiosis can mimic common illnesses such as lymphoma, tuberculosis, sarcoidosis, and other granulomatous infections. Cough, when present, is typically productive of thick mucopurulent sputum. A high index of suspicion in an appropriate clinical setting is required to make the diagnosis.2,3
The lung appears to be the most commonly involved organ, however, disseminated infection involving the brain, muscle, bone, and skin may occur. The infection usually begins in the respiratory tract and 75% of patients exhibit a primary pneumonitis. The radiological manifestations of nocardiosis are variable, including lobar infiltrates or consolidation, thick walled cavities, or solitary nodules. Miliary lesions, adult respiratory distress syndrome, and pleural effusions have also been noted.3,4 When effusions are present, they are almost always associated with parenchymal infiltrates. The fluid can be either serous or purulent and is always exudative as in our patient. Uncommonly, nocardiosis may present as an endobronchial mass lesion as in this case.5–7 The radiological features of mass lesion has a broad differential including a variety of infections such as actinomycosis, fungal infections such as blastomycosis and coccidiodomycosis in endemic areas, bacterial infections such as Staphylococcus aureus, malignancies such as primary bronchial carcinomas and lymphomas.5 In the case described the short history and a productive cough were more suggestive of an infection than a malignancy. Gram staining of the bronchial wash and endobronchial biopsies suggested a diagnosis of nocardiosis. The patient was treated with trimethoprim (10 mg/kg)-sulfamethoxazole (100 mg/kg) two doses a day given orally. Bronchial wash cultures grew N asteroides approximately 20 days after fibreoptic bronchoscopy. The patient responded well to this antimicrobial therapy with complete resolution of clinical and radiographic manifestations of disease after six months. Imipenem, minocycline, cefotaxime, and amikacin may be used as alternative agents in patients with sulphur allergy.
Impaired cell mediated immunity predisposes patients to develop nocardiosis, however it may occur in apparently normal hosts as in the case described.
The clinical manifestations of nocardiosis are diverse. Pulmonary nocardiosis may rarely produce an endobronchial mass lesion and radiological features that can mimic malignancy.