Immune zones in leprosy

Abstract

Leprosy affects mainly those areas of skin which have a relatively lower temperature and are more exposed to trauma. Certain zones like scalp, palms and soles, genitalia, groins, axillae, eyelids, transverse band of skin over lumboscaral area, midline of back and perineum have been described to be immune to the development of lesions in leprosy. But clinical, histological and bacteriological evidence of involvement of these so called immune zones though infrequent have been documented. Hence, these immune zones should be termed as relatively immune, rather than absolutely immune zones of leprosy.

Borderline Tuberculoid leprosy of the scalp mimicking alopecia areata-vitiligo overlap syndrome: A case report

“…The scalp is considered to be a zone of relative immunity to leprosy, owing to its warm temperature and the tension system among the cleavage lines, subcutaneous fat, aponeuroses and muscles, which prevent M leprae from infiltrating this site. 8,10 Still, MB leprosy cases with scalp involvement have been observed from time to time, although scalp involvement is exceedingly rare in PB leprosy, especially leprotic alopecia. Scalp involvement in leprosy can be classified into: 1.…”

“…Involvement of hairy area of scalp. 10 Infiltration, papules, and nodules are the most common lesions when the hair is intact. Alopecia secondary to leprosy is mild and unusual.…”

Diffuse leprosy with "deck-chair" sign

“…It is important to realize that no skin area is an “immune zone” to the invasion of M. leprae , as studies have documented bacteriological and histological evidence of the disease process in clinically uninvolved skin. [ 10 ] Relative sparing of certain areas in lepromatous leprosy is a known finding, but transformation of this finding into a clinically appreciable “deck chair” sign is an interesting observation.…”

Leprosy: An unusual presentation

“…Hence, these zones are termed relatively immune rather than absolutely immune zones of leprosy. [3] Literature search shows that very few cases with hyperpigmented patches in leprosy have been reported so far. Though many different manifestations of leprosy are known, not many reports of atypical and unusual presentations of the disease.…”