More than 125 years after the discovery of M. leprae, the bacillus is yet to be cultivated in vitro. The diagnosis of leprosy is based on a combination of physical examination findings and skin biopsy and/or smear.[17,18] Slit-skin smears can be performed by making a shallow incision in the skin at standard sites (bilateral earlobes, elbows, and knees), as well as from several typical skin lesions. After the incision is made, the inner surface of the wound is scraped with a blade held at a right angle to the incision. Upon scraping, tissue fluid and dermal tissue are obtained and transferred to a clean microscopic slide where a circular smear is made. After the slide is stained with Ziehl–Neelsen carbol-fuchsin and counterstained with methylene blue, the number of acid-fast bacilli viewed under the microscope per oil immersion field is determined and expressed as a "bacteriologic index." This technique may be used to guide multidrug therapy by assessing the bacterial load before and during therapy.
In addition, a full-thickness skin biopsy specimen from the margin of an active lesion can be obtained and the Fite stain used to visualize acid-fast bacilli in the tissue. If another mycobacterial infection is suspected, culture of tissue biopsy material can be performed; growth will exclude M. leprae. Also, a rapid molecular assay using real-time polymerase chain reaction to identify and quantify M. leprae DNA in tissue samples can be performed at laboratory facilities equipped to perform this test, such as the National Hansen's Disease Program (NHDP) Laboratory in Baton Rouge, Louisiana.[21,22]
Pharmacotherapy. 2012;32(1):27-37. © 2012 Pharmacotherapy Publications