Leprosy diagnostic criteria
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Leprosy is a disease with very different clinical presentations, depending on the immune response provided by the host. Therefore it is important to consider the different conditions that may mimic leprosy's presentation, particularly since the diagnosis of leprosy has a very serious psychological and social impact in a someone's life. To minimize the risk of reaching an erroneous diagnosis and inflicting stress and concern in the patient, criteria were developed to guide the diagnosis and this should only be communicated when a reasonable degree of certainty is present.
Diagnostic Criteria
Attending to the historic and social impact of leprosy in the population, a careful assessment of the patient should be made, before advancing the definitive diagnosis of leprosy. Even when suspected in the differential diagnosis, a reasonable degree of certainty is required, before communicating this to the patient.[1]
For the diagnosis of leprosy, at least one of the following signs should be present:[1]
- Confirmed loss of sensation of a hypopigmented or erythematous skin patch. At this point is also important to count the number of skin lesions, in order to classify the type of leprosy, so that adequate therapy regimen may be started.
- A thickened peripheral nerve, with concomitant loss of sensation and/or weakness of the muscles it stimulates.
- Confirmation of acid-fast bacilli in the skin smear, although most people with leprosy will have a negative smear.
When the patient does not fill the above criteria for the diagnosis, three options are available:
- Discuss the case with colleagues specialized in leprosy and refer these cases to a healthcare center specialized in the condition.
- Reevaluate the diagnosis, considering the possibility of another skin disease.
- Wait three to six months and review the skin lesions again; if it is a case of leprosy, loss of sensation may now be observed and MDT can be initiated.
If there is no loss of sensation in the skin lesions and no enlarged nerves but there are nevertheless suspicious signs, such as nodules or swellings on the face or earlobes, or infiltration of the skin, it is important to try and get a skin smear test done. In these circumstances a positive skin smear confirms the diagnosis of leprosy while a negative result (in the absence of other cardinal signs) would, in practice, rule out leprosy. An alternative diagnosis should then be considered.