Monday, January 19, 2009

Mycobacterium tuberculosis & Scrofula

M tuberculosis is an obligate, aerobic, nonspore-forming rod. Humans act as its sole reservoir, and it continues to be a major health problem worldwide. Nearly one third of the global population (ie, 2 billion people), is infected with M tuberculosis and is at risk of developing the disease. An estimated 8 million people develop active tuberculosis (TB) every year; of those cases, about 2 million result in death. More than 90% of global TB cases and deaths occur in the developing world, of which 75% are in the most economically productive age group (15-54 years).

Patient-to-patient transmission typically occurs via inhalation of small aerosols and, in most cases, the disease is confined to the respiratory system. It can, however, affect any organ system, particularly in immunocompromised individuals, in whom it can involve multiple extrapulmonary sites, including the skeleton, gastrointestinal tract, genitourinary tract, and central nervous system (among others). After a period of replication within the lungs, dissemination occurs through the lymphatic and circulatory systems to extrapulmonary sites, including the cervical lymph nodes. Approximately 95% of nodal disease cases in the adult population are caused by M tuberculosis; the remaining cases are caused by atypical Mycobacterium or nontuberculous Mycobacterium (NTM). This is often the case in the pediatric population of the United States, in which over 90% of the cases are caused by NTM; most of those cases result from Mycobacterium avium complex (MAC), which is typically considered a surgical disease. Since antituberculosis antibiotics were first developed in the 1940s, there has been a steady decline in the general prevalence of TB; however, since the mid-1980s, there has been a resurgence in TB cases as a consequence of the acquired immunodeficiency syndrome (AIDS) epidemic, as well as increasing immigration from developing countries. An increase in the number of drug-resistant strains of M tuberculosis has played a role as well.[1,2,4,5,6]

There is evidence that M tuberculosis has been present since antiquity. The mummy of Nesperhan, a priest of the Egyptian god Amun, showed ventral destruction changes of the lower thoracic spine that led to the typical gibbus formation of spinal TB. "Scrofula" is an old term initially used to describe chronic lesions of the head and neck that today are believed to have likely represented TB infection. In 1882, Robert Koch discovered a staining technique that enabled him to isolate the tubercle bacillus, thereby establishing TB as an infectious disease. Head and neck TB is often difficult to diagnose clinically, and it is seldom suspected by clinicians. It is frequently confused for a neoplastic process (as in this case), which results in a delay in treatment. TB of the head and neck represents about 15% of cases of extrapulmonary TB, with about 1.5% of all new cases manifesting in this way. Tuberculous lymphadenitis causes rubbery, painless enlargement of the cervical lymph nodes, usually bilateral, with the posterior cervical chain most commonly involved as well. Lung involvement is most often encountered with lower nodal involvement. If left untreated, the nodes may ulcerate, producing draining sores. Fevers, chills, sweats, and weight loss have been reported to occur in about 20% of individuals. Complications of head and neck disease include scar formation in a draining fistula of the neck, especially after biopsy.


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