Tuberculosis.

Tuberculosis of the skeleton is a pathology that was rare in recent times, except in those areas where there is recent immigration from the third world. Since more than a third of our catchment population is from Gujerat in India, we are used to seeing tuberculosis of bone. The advent of AIDS means that others are now sharing our experience. Since tuberculosis is a disease of malnutrition or sub-nutrition, we should hope that the demographers and politicians can get the numbers right and keep the world food production ahead of our burgeoning population (biofuels for people not overlarge vehicles). A more sobering development is the emergence of antibiotic resistance from undertreatment in a failure of public health provision, either from lack of funding by short-sighted politicians or from that feckless small minority, who do not complete their provided course of treatment.

The causative organism is a mycobacterium. It has a waxy coat, which protects it and some absorbed dyestuffs (carbolfuchsin), giving the other name of acid-fast bacilli. The bacterium divides within the cell, when phagocytosed. It requires oxygen, explaining its preference for the respiratory tract. The primary infection may not always be appreciated from the chest X-ray. Over 50% of the cases of skeletal or bowel tuberculosis may be laryngeal or tracheo-bronchial ulceration. Internal organs and the skeleton are involved by blood borne infection, after vessel invasion from the primary lesion. The pathological process is of accumulation of mononuclear and then giant multinuclear cells with a pseudo-foreign body reaction proceeding to fibrosis and calcification. If this process in the skeleton is not limited early on, the bone destruction is related to the effect of the accumulating pus and its contained chemicals. Calcification will not be a feature in the images, unless there is some immune resistence or anti-tuberculous therapy.

The radiograph will show bone destruction and this process will breach fibrous tissues boundaries more easily than will tumour. Disc space loss would be a characteristic feature of spinal disease, as well as the patches of bone destruction. In Central Middlesex Hospital cases, any bone or joint may be affected. The characteristic feature of tuberculous arthritis as opposed to pyogenic infection is the relative preservation of the weight bearing surfaces and destruction at the joint margins. Perhaps this is a consequence of mechanical pressures and the organism's greater preference for higher effective partial pressures of oxygen.

AIDS affects the very cells that wall off the Tubercle bacilli. Defence includes a combination of the fibrosis and lack of oxygen. Tubercle bacilli, like Toxoplasmosis, can survive (or 'hibernate') in cells. The failure of the cellular mediated immunity will permit re-emergence and recurrence of the pathology often without exposure to a new infection.

See also:

Tuberculosis in the skull.

Pulmonary Tuberculosis

Tuberculosis in the Abdomen