Friday, March 13, 2009

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB) and a member of a group of closely related organisms in the M tuberculosis complex: Mycobacterium africanum, Mycobacterium bovis, Mycobacterium microti, and M tuberculosis. In 1882, Robert Koch discovered and isolated the tubercle bacillus (M tuberculosis). TB is an ancient disease. Signs of skeletal TB (Pott disease) were evident in Europe from Neolithic times (8000 BCE), in ancient Egypt (1000 BCE), and in the pre-Columbian New World. TB was recognized as a contagious disease by the time of Hippocrates (400 BCE), when it was termed "phthisis" (Greek from phthinein, to waste away). World incidence of TB increased with population density and urban development so that by the Industrial Revolution in Europe (1750), it was responsible for more than 25% of adult deaths. Indeed, in the early 20th century, TB was the leading cause of death in the United States. Neil Finsen won the Nobel Prize in Medicine in 1903 for introducing UV light into the treatment of skin TB. With the improvement of living conditions and the introduction of effective treatment (streptomycin) in the late 1940s, the number of reported TB patients in the United States steadily declined (126,000 TB patients in 1944, 84,000 in 1953, 22,000 in 1984, and 14,000 in 2004) despite explosive growth in the total population (140 million people in 1946, 185 million in 1960, and 226 million in 1980).
Cutaneous tuberculosis has a worldwide distribution. In the past, it was more prevalent in temperate countries with cold and humid climate with few hours of daily sunlight but now it is being encountered in tropical countries like India. Malnutrition and low socioeconomic conditions are predisposing factors for cutaneous tuberculosis. Two decades back a decline was observed in the incidence of cutaneous tuberculosis, but recently there is resurgence of cutaneous tuberculosis due to multidrug resistant strains of Mycobacterium tuberculosis. Though human disease with Mycobacterium tuberculosis and is usually spread by droplets and the portal of entry is often the respiratory tract, skin can also be primarily involved. Lupus vulgaris occurs mainly in patients with moderate or high degree of immunity. The lesion arises due to inoculation by exogenous source and by hematogenous spread. Scrofuloderma manifests after the breakdown of the skin overlying a tuberculous focus usually a lymph node but sometimes an infected bone or joint. A patient with moderate or high degree of immunity can develop TBVC if accidental superinfection from extraneous source and autoinocualtion or post-traumatic inoculation with infected sputa occurs. In the present study, out of 51 clinically suspected cases of cutaneous tuberculosis, Scrofuloderma formed the largest group as also reported by other workers. 23.52% cases belonged to Lupus vulgaris and 13.73% cases were of TBVC. Scrofuloderma accounted for the largest number of cases (62.75%). Demonstration of acid fast bacilli in tissue smears by Ziehl Neelsen's staining was possible in 5/51 (9.8%) cases. This conforms with study by Sehgal et al in which 9.52% cases were smear positive. As opined by Montgomery7 and Sehgal et al, it was easy to demonstrate acid fast bacilli in tissue smears in cases of Scrofuloderma. Tissue exudates were found to be better clinical specimens for detection of acid fast bacilli whenever possible as in case of Scrofuloderma cases. Acid fast bacilli were recovered from 7% to 55% of the cases of cutaneous tuberculosis by various workers. The wide difference in the recovery rate may be due to different clinical materials studied in different ways. It was found that tissue exudates from the lesions of Scrofuloderma yielded better isolation of Mycobacteria (75%) whereas skin biopsy even after homogenization with 0.2% bovine albumin without decontamination gave 45.71% isolation. Recovery of acid fast bacilli was possible in 50% cases of Scrofuloderma, 75% cases of Lupus vulgaris and 57.14% cases of TBVC. Two other studies had 52% and 50% isolation rates from cases of Lupus vulgaris respectively. In 7.84% cases, it was possible to both demonstrate and recover acid fast bacilli from clinical specimens of cutaneous tuberculosis. In 49.0%, it was possible to only recover the bacilli whereas demonstration in primary smear was not possible. In one case out of 51, where the patient was treated with antituberculosis drugs of Isoniazid, Rifampicin, Pyrazinamide and Ethambutol, acid fast bacilli were seen in the smear but not isolated in culture. This can be explained as the nonviability of the organism due to prior treatment. Twenty six out of 29 cases, where Mycobacterium spp. were isolated, were Mycobacterium tuberculosis (89.65%). Two out of 3 atypical Mycobacteria were M.scrofulaceum and one was M.avium complex. One M.scrofulaceum and the M.avium complex isolates were recovered from two different immunocompromised patients. This has also been cited by Murray et al, 12 Lombardo et al, and Villas F et al who have isolated M.scrofulaceum and M.avium complex from skin lesions in immunocompromised patients. However one isolate of M.scrofulaceum was isolated from a 10 year old immunocompetent patient having cervical adenitis. Thus, M.tuberculosis was the most common aetiological agent of cutaneous tuberculosis in the morphological variants of Scrofuloderma, Lupus vulgaris and TBVC in the present study though M.scrofulaceum and M.avium complex were also isolated from Scrofuloderma cases which was the most common clinical morphological variant encountered. In the class of tuberculoses of the skin must be placed all those cutaneous lesions which are due to the presence of the bacillus of Koch. Owing to the work of this latter observer, Baumgarten, and many others, we now know that many of the cases formerly called papilloma, anatomic wart, lupus vulgaris, tuberculosis cutis, scrofuloderma, etc, are examples of the one and same process, probably modified by the condition of the patient, the resistance of the tissues, and other factors. The subject of tuberculosis, indeed, is becoming a broad one, and the interest is ever increasing. The gravity of the disease, whether internal or integumentary, is receiving the attention it deserves. Its danger to the community is not yet, however, sufficiently recognized, and the indif¬ference of the individual, the public, and the press to the presence of hundreds of cases of internal tuberculosis contrasts strikingly with the hysteric clamor aroused by the discovery of a single leper in our midst. There have certainly been many cases of cutaneous tuberculosis which could be traced directly or indirectly to another in the family having the constitutional disease, which, with other evidence, will be touched upon again in considering etiology. While many clinical phases have been reported in recent years, the cases of tuberculosis of the skin can prac¬tically be included under five heads:
1. Tuberculosis ulcerosa;
2. Tuber¬culosis disseminata;
3. Tuberculosis verrucosa;
4. Scrofuloderma;
5. Lupus vulgaris.
The first two are extremely rare, the third uncommon, the fourth not unusual, and the last—lupus vulgaris—relatively quite frequent. These various types deserve separate clinical description; consideration of their etiology, pathology, and detailed methods of treat¬ment will follow the last.
United States
Alarmingly, the number of reported patients with TB in the United States has been increasing since 1985 such that TB has reemerged as a serious national problem. In 1998, researchers reported 18,361 patients with TB; the rate of TB infection was 6.8 cases per 100,000 population. California, Florida, Illinois, New York, and Texas reported 54% of TB occurrences. The proportion of TB patients who were foreign-born individuals was 42%. Persons born in Mexico, the Philippines, and Vietnam account for one half of foreign-born TB patients in the United States. The TB rate among foreign-born persons was 4-6 times higher than for US-born persons. Minimum estimates of the proportion of TB patients with coincident HIV infection were approximately 10-15%. Among persons aged 25-44 years, this proportion increased to 20-30%. The underlying basis of this new TB epidemic reflects a minimum of four major factors including (1) the association of TB with the HIV epidemic, (2) increased immigration from countries where TB is common, (3) transmission of TB in congested settings (health-care facilities, prisons, homeless shelters), and (4) the deterioration of basic health-care infrastructure. Molecular typing of M tuberculosis isolates in the United States by restriction fragment-length polymorphism analysis suggests more than one third of new patient occurrences result from person-to-person transmission, and the remainder result from reactivation of latent infection. Approximately 1 of 13 M tuberculosis isolates currently shows a form of drug resistance. The recent introduction of biological agents that block tumor necrosis factor-alpha in the treatment of rheumatoid arthritis, psoriasis, and several other autoimmune disorders has further raised concern for the identification of patients with latent TB. Currently, several hundred cases of TB disease have been reported in patients who receive these tumor necrosis factor-alpha antagonists.
The current global burden of TB boggles the mind. In 1997, the incidence of new TB patients approached 8 million in addition to more than 16 million existing patients. Approximately 2 million people died of TB in 1997 with a global fatality rate of 23% (fatality rates exceed 50% in some African countries with high HIV incidence). The estimate of the proportion of TB patients with coincident HIV infection is approximately 8%. Among infectious diseases, TB is the leading cause of death. TB was responsible for 6% of deaths worldwide. Global prevalence of TB currently is greater than 32%. More than 50% of new patient occurrences were in 5 Asian countries, ie, India (largest worldwide patient load), China, Indonesia, Bangladesh, and Pakistan.
Male-to-female ratio is 1.35:1.
Although no age group is exempt, most patients show clinical infection within the first 3 decades of life.
What tests are available?
The diagnosis is usually made or confirmed by skin biopsy. Typical tubercles are caseating epithelioid granulomas that contain acid-fast bacilli. Other tests that may be necessary include:
• Tuberculin skin test (Mantoux)
• Sputum culture (it may take a month or longer for results to be reported)
• Chest X-ray & other radiological tests for extrapulmonary infection.
What is the treatment of cutaneous TB?
Patients with pulmonary or extrapulmonary TB disease need to be treated with antitubercular drugs. This usually involves a combination of antibiotics (isoniazid, rifampicin, pyrazinamide and ethambutol) given over a period of several months and sometimes years. Patients with TB infection but no active disease must also be treated with antitubercular drugs to prevent development of active disease. Occasionally surgical excision of localised cutaneous TB is recommended.


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