Written by epgonline.org - Last updated 29 May 2018
Tuberculosis (TB) is an umbrella term for infection with mycobacterium tuberculosis, an organism which has existed alongside humans for thousands of years, with DNA evidence identified in Neolithic remains dating from around 9000 years ago. With the development of antibiotics and vaccines against TB, there were hopes that elimination of the disease was imminent. However, drug resistance, coupled with HIV co-infection and increasing use of immunosuppressants, led to a relative resurgence in the late 20th century.
WHO figures from 2016 suggest that approximately one third of the world’s population (95% of which is in the developing world) is infected with latent TB.
The pathogen is slowly replicating, has a characteristic cell wall, and survives being engulfed by host macrophages, within which it replicates, typically resulting in an indolent infection. Tuberculosis was so named for the “tubercles” seen pathologically. These are granulomatous, spheroid lesions consisting of a central area of necrosis, an interstitial area with a high concentration of macrophages and an outer zone consisting of lymphocytes, monocytes and plasma cells. These lesions act as reservoirs of chronic infection.
Pulmonary infection is the most common manifestation, and airborne transfer the primary mode of transmission. It typically presents with persistent pyrexia, associated with a variety of other symptoms directly relatable to the lungs, such as pleuritic pain, pleural effusion or cough with bloodstained sputum.
Extrapulmonary TB can spread to anywhere in the body; the most likely sites of blood-borne metastasis are the pleura, lymphatic system, central nervous system, genito-urinary tract and bone. As a result, the clinical picture can be highly variable.
Miliary tuberculosis is a more acute and disseminated variant of the infection. It has a high mortality rate, presenting most commonly in younger or immunocompromised patients, and can be difficult to diagnose early due to its non-specific presentation.