The clinical findings are varied, and many organs can be involved, but the lungs are the main site of infection. Constitutional symptoms such as fever, fatigue, night sweats, and weight loss are common. Anemia of chronic infection can occur.
In pulmonary tuberculosis, the main findings are cough and hemoptysis. The chest X-ray findings in reactivation tuberculosis of the lung include an infiltrate in the upper lobe with or without a cavity.
Scrofula is mycobacterial cervical lymphadenitis that presents as swollen, nontender lymph nodes, usually unilaterally. M. tuberculosis causes most cases of scrofula, but nontuberculous mycobacteria (NTM), such as Mycobacterium scrofulaceum, can also cause scrofula. Lymphadenitis is the most common extra pulmonary manifestation of tuberculosis. Patients infected with human immunodeficiency virus (HIV) are more likely to have multifocal lymphadenitis than those not infected with HIV.
Erythema nodosum, characterized by tender nodules along the extensor surfaces of the tibia and ulna, is a manifestation of primary infection seen in patients who are controlling the infection with a potent cell-mediated response. Miliary tuberculosis is characterized by multiple disseminated lesions that resemble millet seeds. Tuberculous meningitis and tuberculous osteomyelitis, especially vertebral osteomyelitis (Pott’s disease), are important disseminated forms.
Gastrointestinal tuberculosis is characterized by abdominal pain and diarrhea accompanied by more generalized symptoms of fever and weight loss. Intestinal obstruction or hemorrhage may occur. The ileocecal region is the site most often involved. Tuberculosis of the gastrointestinal tract can be caused by either M. tuberculosis when it is swallowed after being coughed up from a lung lesion or by M. bovis when it is ingested in unpasteurized milk products. Oropharyngeal tuberculosis typically presents as a painless ulcer accompanied by local adenopathy.
In renal tuberculosis, dysuria, hematuria, and flank pain occur. “Sterile pyuria” is a characteristic finding. The urine contains white blood cells, but cultures for the common urinary tract bacterial pathogens show no growth. However, mycobacterial cultures are often positive.
Note that most (approximately 90%) infections with M. tuberculosis are asymptomatic. Asymptomatic infections, also known as latent infections, can reactivate and cause symptomatic tuberculosis. The most important predisposing factor to overt disease is a host’s reduced cell-mediated immune (CMI) response. For example, AIDS patients have a very high rate of reactivation of prior asymptomatic infection and of rapid progression of the disease. In these patients, untreated disease caused by M. tuberculosis has a 50% mortality rate.
Furthermore, administration of infliximab (Remicade), a monoclonal antibody that neutralizes tumor necrosis fac tor (TNF), has activated latent tuberculosis in some patients. The explanation for this is that TNF activates helper T cells to make gamma-interferon that activates macrophages to kill M. tuberculosis. So if TNF is neutralized by infliximab then gamma-interferon is not made and killing of M. tuberculosis by macrophages is reduced. Remicade is used in the treatment of rheumatoid arthritis. Diabetics are also predisposed to reactivation and progression of disease.
In some patients with AIDS who are infected with M. tuberculosis, treating the patient with antiretroviral therapy (ART) causes an exacerbation of symptoms. This phenomenon is called immune reconstitution inflammatory syndrome (IRIS). The explanation of the exacerbation of symptoms is that ART increases the number of CD4 cells, which increases the inflammatory response. To prevent this, patients should be treated for the underlying infection before starting ART.
Asymptomatic adults who are at high risk of having a latent infection should be screened using either the PPD skin test or the interferon-γ release assay (IGRA) test. Examples of adults at high risk are those who have lived in countries with increased prevalence of tuberculosis and those who are homeless. If found to be positive, these patients should be treated for latent infection. Screening tests and the treatment of latent infections are described later in this chapter.
