lists of suitable labs for slit-skin smear examination in leprosy

Leprosy Mailing List – October 3^rd, 2011

Ref.:    It would be advisable to provide, lists of suitable labs for slit-skin smear examination in leprosy.From:  Warren G, Sidney, Australia

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Dear Dr Noto,

I am very pleased to read the comments on slit skin smears made by Dr Barreto (LML Oct. 2^nd 2011).  Many times I have found that smears were reported as negative and when rechecked it was found that the stain was not correctly done.

Yes, M. leprae is difficult to stain and easily over decolourised by the use of the wrong acid-alcohol mixture.  This is particularly a problem when slides are sent for acid fast bacilli (AFB) examination to a good lab that does not do M. leprae as a routine.  So I must confess that if I diagnose leprosy and feel the patients ought to have a positive smear I often also send a suitable slide to an experienced lab to be sure, if it is said to be negative by the first lab.

I have had some very embarrassing experiences with laboratory personnel, whom one would think would be reliable, giving negative diagnosis on a patient who is clinically clearly positive.  It is even more embarrassing when pathologists cannot diagnose from a fairly typical biopsy as happened with one patient with a definite red line (typical of BB) where the anaesthesia started – and when we looked at the stained biopsy a relatively inexperienced pathologist spotted the AFB at once but the Professor at the first institute had not seen them and had stated emphatically it was not leprosy.

It is important that we hone our ability to diagnose so that patients with leprosy are not deprived of MDT and the possibility of recovery without deformity.  I have seen many “primary persistent neuritic leprosy” patients who have early ulnar nerve lesions (clawing of fingers) but NO skin lesions and are dismissed by WHO personnel as “not leprosy” because no anaesthetic skin lesion.  Yet in S E Asia these are common and a biopsy of the nerve will prove AFB etc. present - but many places do not have those facilities.  In fact many clinics in third world countries have no facilities to do slit skin smears and may even have no suitable place to send slides on for examination.  We must hone our ability to diagnose by clinical signs and history.

Would it be advisable to provide, lists of the suitable labs who would check slit skin smears and/or biopsies for those who need it and may be make sure all the labs have full detailed instructions of the correct methods and strengths of stains to get reliable results.

Grace Warren  

Previously adviser for the Leprosy Mission in Asia.