Leprosy (Hansen disease, Mycobacterium leprae infection)
Leprosy (Hansen disease) is a chronic granulomatous infection of skin and peripheral nerves caused by the acid-fast bacillus Mycobacterium leprae, spanning a tuberculoid-to-lepromatous immune spectrum, diagnosed by hypopigmented anesthetic skin lesions with thickened nerves confirmed on skin smear or biopsy, and cured with WHO multidrug therapy.
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What this article covers
- Overview
A chronic granulomatous infection of the skin and peripheral nerves caused by Mycobacterium leprae, an obligate intracellular, acid-fast bacillus that cannot be cultured in vitro and prefers cool body temperatures.
- Epidemiology
Endemic in resource-limited tropical and subtropical countries, with the largest disease burden in India, Brazil, and Indonesia; transmission requires prolonged close contact, so incidence is low in high-income countries.
- Risk factors
Prolonged close household contact with an untreated multibacillary (lepromatous) leprosy patient, the dominant risk factor.
- Pathophysiology
Mycobacterium leprae is an obligate intracellular acid-fast bacillus that infects Schwann cells and dermal macrophages, with tropism for cool body sites, producing the classic distribution in skin…
- Clinical features
The hallmark finding is one or more hypopigmented or erythematous skin patches or plaques with definite sensory loss (light touch and pinprick) within the lesion, distinguishing leprosy from other…
- Differential diagnosis
Tinea versicolor: hypopigmented, finely scaling truncal macules confirmed by potassium hydroxide preparation showing hyphae and yeast ("spaghetti and meatballs"); sensation is intact, unlike a leprosy patch.
- Diagnosis
Leprosy is a clinical diagnosis confirmed by at least one of three cardinal signs: a hypopigmented or reddish skin lesion with definite sensory loss, a thickened peripheral nerve with loss of…
- Management
First, classify the patient as paucibacillary or multibacillary based on lesion count and skin-smear result, since this sets the multidrug therapy regimen and duration; treatment is always combination therapy to prevent drug resistance.
- Complications
Permanent peripheral nerve damage and deformity: claw hand, wrist or foot drop, and facial nerve palsy with lagophthalmos, often irreversible once established.
- Prognosis
Leprosy is curable with multidrug therapy, and relapse after a completed course is uncommon.
- Prevention
Single-dose rifampin post-exposure prophylaxis (600 mg PO once for adults, weight-adjusted for children) is recommended for household and close contacts of a newly diagnosed patient to reduce their risk of developing disease.
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