Contributor: Gordon K. Klintworth
Tuberculosis can be either primary or secondary. Primary tuberculosis represents the initial infection by Mycobacterium tuberculosis and it is characterized by the Ghon complex . It is usually asymptomatic and seldom progresses to a clinical syndrome. Cavitation is not a feature of primary tuberculosis. Spread of tuberculosis by lymphatics and hematogenously can result in miliary tuberculosis that is seeding of distal organs. Secondary tuberculosis is activation of the Ghon complex and the bacteria often becomes disseminated through the blood stream and by the lymphatics. Miliary tuberculosis can result. Reactivation tuberculosis occurs especially in immunocompromised individuals (including those with AIDS) and elderly, malnourished persons when a tubercle breaks down and bacilli disseminate. Fever, hemoptysis, a bloody pleural effusion, and wasting are common. The lesions are usually in the apical or posterior parts of the upper lobes and they may coalesce and ruptures, producing a cavitary lesions. There is also scarring and calcification. Extrapulmonary lesions in tuberculosis include meningitis, Pott disease, paravertebral abscess and psoas abscess. Ocular manifestations in tuberculosis mostly consist of phlyctenular keratoconjunctivitis [keratoconjunctivitis - phyctenular], iritis, cyclitis, choroidal nodules, retinitis, and endophthalmitis. Children may have an incidental positive PPD. The charcteristic lesion is the tubercle with central caseous necrosis and Langerhans giant cells. Healed tubercles remain stable for years and often become calcified. Tuberculosis should be considered in the differential diagnosis of unilateral conjunctivitis with preauricular lymphadenopathy. The tuberculin test is used in the diagnosis of tuberculosis.