• Volume 70 , Number 1
  • Page: 36–7

"A natural sweat test" in leprosy

Sunil Dogra; Abir Saraswat; Inderjeet Kaur; Bhushan Kumar

To the Editor:

Leprosy is a chronic infectious disease with varied presentations. Nerve involvement is undoubtedly of fundamental importance in the pathogenesis of leprosy. Apart from motor paralysis and sensory loss, autonomic neuropathy is reported in varying degrees as indicated by sweat function tests, histamine triple response and tests for cardiovascular and respiratory system involvement in leprosy (4). It has been observed that on the anesthetic areas of leprosy the lesions of psoriasis either do not occur or disappear because degenerated dermal nerve fibers cannot produce neuropeptides like substance P, vasoactive intestinal peptide (VIP) and calcitonin G related peptide (CGRP) which are essential for neurogenic inflammation in the pathogenesis of psoriasis (5). The lack of sweating in lesions of leprosy which is wellknown, also confirms the destruction of nerves in the infiltrates of leprosy (4). Recently we noticed an interesting finding of miliaria rubra sparing lesions of leprosy, which again can be explained on the basis of neural involvement in leprosy.

A 20-year-old male patient, an established case of borderline leprosy (BL) under treatment, complained of extremely pruritic lesions over his trunk which on examination were found to be miliaria rubra. During the examination the most noticeable finding was complete sparing of leprosy patches by the lesions of the miliaria rubra (The Figure). The multiple anhidrotic leprosy lesions were dramatically highlighted by a 'natural sweat test' which resulted in the production of the lesions of miliaria rubra. There was no other abnormality of any nature detected on systemic or cutaneous examination.


The Figure. Extensive miliaria rubra over back sparing leprosy patches.


Miliaria rubra is a condition in which free flow of eccrine sweat to the skin is impeded. It is commonly seen in hot humid environments which result in injury to the epidermal cells lining the eccrine duct producing keratinous plugging. It presents as small, discrete, erythematous papulovesicles with a predilection for the clothed areas of the body (1). Leprosy lesions are known to be anhidrotic due to the destruction of sweat glands by local infiltrate around them and perineural granuloma resulting in autonomic nerve damage (2). A useful adjunct to the early diagnosis of a leprosy lesion is a sweat test, which is usually done using pilocarpine nitrate injected intradermally. The leprosy lesions become obvious being hypohidrotic or anhidrotic (3). The absence of miliaria rubra over leprosy lesions in our patient can be attributed to the reduced or absent functioning of sweat glands, which plays a central role in the pathogenesis of miliaria. This phenomenon is perhaps common in the hot humid climate of the Indian subcontinent, but has probably gone unnoticed in the past. Its explanation lies in the basic pathological changes which occur in and around nerves and appendages. To the best of our knowledge this observation has not been reported in the past.


- Sunil Dogra, M.D., DNB
Abir Saraswat, M.D.
Inderjeet Kaur, M.D., MNAMS
Bhushan Kumar, M.D., MNAMS

Department of Dermatology, Venereology and Leprology
Postgraduate Institute of Medical Education and Reseurch
Chandigarh, India




1. CHAMPION, R. H. Disorders of sweat glands. In: Textbook of Dermatology. Champion, R. H., Burton, J. L., Burns, J. L., Breathnach, S. M eds. 6th edn. Oxford: Blackwell Science, 1998, pp. 1985-2002.

2. JOB, C. K. Pathology of leprosy. In: Leprosy. Hastings, R. C., ed. 2nd edn. Singapore: Churchill Livingstone. 1994, pp. 193-224.

3. JOPLING, W. H. Diagnostic tests. In: Handbook of Leprosy. 2nd edn. Jopling, W. H.. ed. London: William Heinmann Medical Books Ltd., 1978. pp. 50-55.

4. RAMACHANDRAN, A. and NEELAN, P. N. Autonomic neuropathy in leprosy. Indian J. Lepr. 59(1987)405-413.

5. RAYCHAUDURI, S. P. and FARBER, E. M. Neuropeptides and neurogenic inflammation in psoriasis. In: Psoriasis. 3rd edn. Roenigk, H. H. Jr. and Maibach, H. I., eds. New York: Marcel Dekker. Inc.. 1998, pp. 383-397.











Address for correspondence:
Dr. Bhushan Kumar. Prof. & Head
Dept. of Dermatology, Venereology & Leprology, PGIMER
Chandigarh-160 012, India
Fax: +91 (0172) 744401, 745078
e-mail: kumarbhushan@hotmail.com

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