Skin Lesions with Minimal or Doubtful Sensory Impairment—Better to Defer Biopsy?

Dear Editor,

I read with interest the article “Hypopigmented skin lesions with doubtful/minimal sensory impairment: a histopathology-based analysis” by Sasidharanpillai et al.[1] The authors deserve appreciation for bringing out a real-life situation in the diagnosis of indeterminate leprosy. Here, I wish to advance the discussion on how cases of hypopigmented skin lesions with doubtful or minimal sensory impairment may be managed.

One of the three cardinal criteria for diagnosis of leprosy is a definite loss of sensation of the skin patch—the other two being those related to nerve thickening and demonstration of acid-fast bacilli (AFB).[2] The emphasis is on definite, not on complete. Hence, this case definition cannot include skin lesions with doubtful sensory impairment but could include those with mild, minimal, or slight sensory loss, provided it is definite.

There are mainly two types of leprosy in which the skin lesions may have normal sensations. One is indeterminate leprosy. The diagnostic problem in this type is that they may also lack the other two cardinal features—definite nerve thickening and the presence of AFB. The other is lepromatous leprosy. As these patients have numerous skin lesions, at least a few may demonstrate sensory impairment, especially if the disease is advanced. In any case, AFB will be positive in lepromatous leprosy, which will fulfill one criterion unequivocally.

In the case series presented by the authors, 50% of the patients suspected to have indeterminate leprosy (7 out of 13 with skin lesions with minimal sensory impairment and one out of three with doubtful sensory impairment) had no histopathological evidence of it. It would be interesting to know the outcome of these patients on the follow-up—whether they develop definite features of leprosy or other diseases, continue to have minimal or doubtful sensory impairment; or the lesions resolve.

This being a retrospective analysis, it is difficult to ascertain if the examination was standardized—in terms of the methods used and the experience of the examiners. The distinction between minimal and doubtful sensory impairment could be subjective. It is natural that histopathological examination would yield inconclusive results in a sizable proportion of such patients.

Is it possible to decrease the frequency of such cases remaining inconclusive even after the histopathological examination? One strategy is to re-examine such patients any number of times as needed, especially by experienced clinicians, and proceed with histopathological examination only if there is a reasonable consensus about definite sensory impairment, albeit partial. This approach would be in line with the maxim in diagnosing leprosy: when in doubt, never diagnose leprosy.[3] It would also lead to more definite decisions in a type of disease that is truly indeterminate clinically and histopathologically. In the current context of a decrease in the caseload of leprosy in the community, with non-leprosy differentials often outnumbering leprosy, this approach may be more relevant.

Would postponing the biopsy lead to bad outcomes in those cases that later turn out to be leprosy? Probably not, because, as long as the skin smear is negative for AFB, there is no appreciable risk to the patients or the contacts by delaying the diagnosis until it is definite. It may also be noted that a sizable proportion of patients with indeterminate leprosy heal spontaneously.[3]

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