Q1: What do the chest radiograph and orbital MRI scan show? Give a differential diagnosis for the radiological findings

The chest radiograph (see p 601) shows paratracheal lymphadenopathy, and the orbital MRI scan (see p 601) shows a mass around the left optic nerve. The differential diagnosis of these radiological findings would include sarcoid, tuberculosis, other infections such as brucella, toxoplasmosis and fungi, and also lymphoma and other malignancies.

Q2: What investigation would give the diagnosis?

Bronchoscopy. The likely diagnosis in this women of African origin with systemic symptoms, mediastinal lymphadenopathy, and masses elsewhere is tuberculosis. Bronchoscopy is particularly appropriate in the presence of stridor and also because most patients with suspected tuberculosis who have only mediastinal lymphadenopathy and no lung shadowing are smear negative on sputum samples.

In this case, bronchoscopy revealed copious white (caseous) material infiltrating the right main bronchus, presumably from an adjacent lymph node. In older subjects it can be difficult to distinguish macroscopically between tuberculosis and carcinoma. Histology in this patient demonstrated caseating granulomata with acid fast bacilli. Culture confirmed that the organism wasMycobacterium tuberculosis, fully sensitive to all first line drugs. Mediastinoscopy or trans-sphenoidal biopsy of the lesion on the optic nerve would be further options for diagnosis.

Q3: What other serology would be helpful?

HIV serology. In the young African population HIV infection is an increasingly common cause of malaise, weight loss, fever, and isolated mediastinal lymphadenopathy. Once tuberculosis has been confirmed the issue of HIV seropositivity must be considered, with the increasing rates of co-infection in the African population.1 2 It has implications not only for future therapy, but also raises questions about the nature of the optic nerve lesion. In the immunocompetent host the mass could confidently be labelled a tuberculoma. However, in the compromised patient other conditions such as fungal infections, syphilitic gummas, toxoplasmosis, lymphoma, and other malignancies are possibilities and definite histology would be needed for accurate diagnosis.

Our patient had multiple risk factors for HIV infection, but was antibody negative. For this reason and also because the optic nerve mass lay close to the carotid artery, the lesion was not biopsied. It was assumed to represent a tuberculoma, and its size monitored during treatment on serial MRI scans.

Outcome

The patient was initially treated with standard antituberculous therapy except for streptomycin instead of ethambutol to avoid visual complications. Once the mycobacterium was found to be fully sensitive, the streptomycin was stopped. Although vision in the affected eye failed to improve, the patient improved systemically and made a good recovery.

Discussion

Involvement of the central nervous system occurs in about 10% of all patients with tuberculosis.3 The most common form is meningitis, although encephalopathy, abscesses and tuberculomas also occur, the latter especially in patients with impaired cell mediated immunity.1 On computed tomography tuberculomas appear as ring enhancing lesions which may be difficult to differentiate from toxoplasmosis or neurocysticercosis, particularly in India where both tuberculosis and cysticercosis are endemic.4 MRI can be helpful, although stereotactic biopsy may be necessary for accurate diagnosis. A further problem is that tuberculomas may enlarge or develop during treatment, often raising questions about diagnosis and requiring steroid therapy or even surgical management.5

The increasing incidence of tuberculosis worldwide is largely due to the rising prevalence of HIV infection.1 Clinical presentation in the HIV positive patient depends on the degree of immunocompromise. Early on, tuberculosis resembles typical post-primary disease with predominant lung involvement. As the CD4 count falls, the presentation becomes more non-specific, with weight loss, fevers, malaise, and manifestations of extrapulmonary disease.2 To further confound the diagnosis, these patients are frequently sputum smear negative, the chest radiograph may only show mediastinal lymphadenopathy, and the tuberculin skin test is negative.

Treatment of tuberculosis with HIV co-infection is with conventional antituberculous agents. Although the clinical response is good, survival is poor, especially with central nervous system involvement.

Final diagnosis

Tuberculosis with optic nerve tuberculoma.