Case report: A 45 year old black woman with recurrent, chronic ulcerative skin lesions of the left lower leg, refractory to multiple courses of antibiotics was referred to The JHH Dermatology Clinic for further evaluation. The patient first noted the development of these ulcers three years ago in the Spring of '95. She attributed these left lower leg lesions to insect bites acquired while walking outside near her home in suburban Maryland. The patient was admitted for IV antibiotic therapy since the ulcerous lesions worsened over the next few months. By report, skin biopsies from the initial lesions showed multiple non-caseating epithelioid granulomata of the superficial and deep dermis and associated mild chronic inflammation. Special stains and cultures were not obtained at that time. The skin lesions improved with antibiotic therapy, but never seemed to clear entirely. In the course of three years this patient was admitted annually for wound care and IV antibiotic therapy, which included Augmentin and ciprofloxacin. The most recent admission was 2/98 and since 3/98 she has been treated with the above antibiotics, currently via portacath. The patient is a former nurse with no significant medical history, exposures, or travels. She is HIV negative and a PPD placed six months prior to the onset of these lesions was also negative. Upon evaluation at The JHH dermatology clinic the patient was afebrile. Examination of the left lower extremity showed multiple various-sized weeping and purulent ulcers with irregular borders, adjacent soft tissue edema and skin fibrosis. The lesions were painful and there was associated left inguinal lymphadenopathy. Results from routine laboratory studies and the chest x-ray were normal. Specifically, there was no evidence of pulmonary sarcoidosis or tuberculosis, inflammatory bowel disease, collagen vascular disease, diabetes mellitus, underlying malignancy or immunodeficiency. A repeat biopsy again showed multiple dermal granulomata and special stains for fungus and acid fast bacteria (AFB) were negative. Cultures for mycobacteria and fungus were sent. An acid fast Mycobacterium species was identified on day 11 growing in culture.

Organism: Chromatographic analysis and a DNA probe were both positive for M. tuberculosis and M. tuberculosis complex, respectively providing early identification and confirmation of culture results. The mycobacteria are aerobic, nonsporeforming, nonmotile, slow growing bacilli. Their characteristic cell wall has a high lipid content that includes waxes with long chain fatty acids or mycolic acids, which account for the organism's acid-fastness. Most mycobacterium species are free living in soil and water, but the major ecological niche for others such as M. tuberculosis is diseased tissues of humans and other warm-blooded animals. M. tuberculosis is transmitted from person to person by respiratory aerosol.

Clinical Manifestations: The usual site of disease of M. tuberculosis is the lungs, but other extrapulmonary sites may be involved. Rarely M. tuberculosis can cause cutaneous conditions. Cutaneous tuberculosis is associated with an immunocompromised state and is usually found in patients with long-standing or untreated disease elsewhere. Clinically, cutaneous tuberculosis can show great variability including red-brown macular lesions, subcutaneous nodules, ulcerous lesions and abscess formations. Additionally, in the case of cutaneous tuberculosis, lesions are often paucibacillary and acid fast bacteria are rarely identified microscopically using special AFB stains. Because cutaneous tuberculosis remains an important differential diagnosis of granulomatous processes in the skin, reliable laboratory tests are needed to confirm or rule out the diagnosis.

Laboratory Diagnosis: Traditionally mycobacteria are identified by traits such as growth rate, colony morphology, pigmentation and further differentiated using biochemical profiles. M. tuberculosis is slow growing, nonphotochromogenic, niacin and nitrate reductase positive with rough colony morphology. While these methods are well established and reliable, they are very slow in providing clinical data. In this case, chromatographic analysis and DNA probes confirmed mycobacterial growth from primary cultures and provided rapid identification. DNA probes can be used to identify isolates on solid culture media or from broth culture and assay results are complete in two hours. The tests can be performed with growth from primary cultures whereas biochemical testing requires inoculation of subcultures causing a further significant delay in testing. While probes offer a rapid and accurate means of isolate identification, poor sensitivity precludes their use for direct detection of Mycobacteria spp. in clinical specimens. Of note, the M. tuberculosis complex probe does not differentiate between M. tuberculosis, M. bovis, M. bovis BCG, M. africanum and M. microti. More recently chromatographic methods using a commercially available identification system have provided highly reliable and specific identification of Mycobacteria spp. in less than two hours. Other laboratory methods including PCR based assays for direct detection and identification of M. tuberculosis in clinical specimens are currently being investigated and are undergoing clinical evaluation.

The diagnosis of M. tuberculosis has serious clinical and epidemiological implications and requires long-term multi-drug antibiotic therapy based on culture sensitivities. Given the immunocompetent state of the patient in this case, the diagnosis of primary cutaneous M. tuberculosis is quite unusual. Therefore, DNA sequencing, which characterizes specific strains of M. tuberculosis, will be performed on this patient's specimen and the other positive M. tuberculosis culture that was received and processed the same day as this patient's in order to rule out the possibility of cross contamination from a single strain.