Leprosy Mailing List – July 18 , 2014
Ref.: (LML) Staining of M. leprae vs. M. tuberculosis and decolorizing with hydrochloric acid
From: Richard de Soldenhof,Edinburgh, Scotland
Dear Pieter,
Dr. Ben Naafs’ comment reinforces the need to ensure that the Ziehl-Neelsen (Z-N) staining procedure on leprosy skin smears is not too robust. As pointed out by Dr. Noto, it has long been stated that M. leprae is more easily decolourised than M. tuberculosis, and hence the 2 commonly used decolourisers, (1% hydrochloric acid in 70% ethanol or 5% sulphuric acid, for M. leprae) are both weaker and are applied to the slide for a shorter period, than for M. tuberculosis.
Our paper, “Choosing the decolouriser and its strength to stain Mycobacterium leprae. Does it matter?” (de Soldenhoff, Hatta and Siro), in Lepr. Rev. 1998 June; 69(2): 128-133, answered this question with a “no”, but Naafs’ report suggests that it is “yes”. It would be of use to have further studies to further clarify this. The other points made in our paper, however, do justify repeating:
• Most new leprosy patients can be competently diagnosed and commenced on appropriate treatment without a skin smear. However, there are some patients who present with single or few lesions, but who have early multibacillary disease. A positive skin smear will be found in some of these patients and this means MB MDT is needed.
• There are other patients, either new or old, who have no clearly demonstrable clinical cardinal signs, but who have a positive smear. In new patients this confirms the diagnosis of multibacillary leprosy; in previously treated patients, it may suggest relapse and a repeat course of MB MDT may be indicated.
• With fewer leprosy patients in a programme which has been officially eliminated, the taking, staining and reporting of leprosy slit skin smears has, in many cases, become a lost art. On the other hand, laboratories at sub district level are usually carrying out Z-N staining for tuberculosis, and there is often a quality control system in place for this.
• Even if the staining technique is not identical, the comparatively small leprosy workload (compared to that for tuberculosis) should make it possible for the same laboratory staff to do both procedures, and of reasonable quality. Taking a skin smear should be within the competence of leprosy field supervisors, as well as of laboratory staff.
Dr. Richard de Soldenhoff,
formerly Leprologist with NLR,
Edinburgh, Scotland, UK
LML - S Deepak, B Naafs, S Noto and P Schreuder
LML blog link: http://leprosymailinglist.blogspot.it/
Contact: Dr Pieter Schreuder << editorlml@gmail.com
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