Overview
Leprosy is a granulomatous infection of the skin and peripheral nerves caused by Mycobacterium leprae, a Gram-positive, aerobic rod that is often found in clumps or groups. There are two presentations that depend on the degree of the immune response:
- Lepromatous (multibacillary) leprosy – low degree, weaker Th2 response, more severe disease
- Tuberculoid (paucibacillary) leprosy – high degree, strong Th1 response, less severe disease
Pathophysiology
It is thought that Mycobacterium leprae is transmitted via the respiratory route and tends to spread to cooler, superficial regions of the body, hence why it spreads to the skin and superficial nerves. It attacks Schwann cells of peripheral nerves causing demyelination, resulting in numbness and reduced autonomic function (e.g. impaired sweating). This alongside its tendency to spread to the skin can cause skin lesions.
The intensity of the immune response correlates with the signs and symptoms seen. People with lepromatous leprosy have disseminated disease due to a weaker immune response, characterised by the production of Th2 cytokines, suppressed macrophage activity, and increased regulatory T-cells. People with tuberculoid leprosy have localised disease due to a stronger immune response, characterised by the production of Th1 cytokines, and increased macrophage activity.
Epidemiology
- Leprosy mainly affects countries in the tropics
- Between 2011 and 2020, there were 75 reported cases of leprosy in the UK
Risk Factors
- Close contact with a person with infection
- Poverty
- Travelling/living in an endemic area
Presentation
Overview
The main features of leprosy include:
- Skin features – hypopigmented patches, often on the buttocks, face, and extensor surfaces, hair loss
- Sensory loss – due to demyelination of peripheral sensory nerves
Lepromatous leprosy tends to have extensive skin and symmetrical nerve involvement, whereas tuberculoid leprosy tends to affect a limited region of skin and nerves are affected asymmetrically.
Investigations
Overview
Its diagnosis is confirmed clinically, however, a skin biopsy and culture can identify Mycobacterium leprae.
Management
Overview
The World Health Organisation (WHO) recommends triple therapy with:
- Rifampicin
- Clofazimine
- Dapsone
