Tuberculosis. Clinical aspects and diagnosis.

The presentation of tuberculosis is variable depending on the severity of the infection, the age of the patient, whether the infection is primary or secondary, and whether the manifestations are due to inhalation of organisms or hematogenous dissemination. A definitive diagnosis is made by culture of the organism; spontaneously expectorated sputum is the most suitable specimen for diagnosing pulmonary tuberculosis. Diagnosis of extrapulmonary tuberculosis frequently requires tissue biopsy. The classic staining method for demonstrating tubercle bacilli is the Ziehl-Neelsen technique. Newer methods based on fluorescent dyes and phase-contract microscopy make rapid screening feasible, but false-positive identification is more frequent. Culture of tubercle bacilli is most successful when two media are used. The differential diagnosis of pulmonary tuberculosis includes bacterial pneumonia, especially anaerobic infection, and fungal infections including histoplasmosis, coccidioidomycosis, and blastomycosis. Lung carcinoma can mimic tuberculosis and the two diseases can coexist. Surgery is frequently necessary for a definitive diagnosis, expecially when the disease is seen as a noncalcified nodule.