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Leprosy and cutaneous mycobacterial infections
Mycobacteria cause chronic skin infections that respond slowly and do not respond to routine antibiotics; in leprosy (M. leprae) disease severity is set by the immune response, and M. marinum causes nodules along the lymphatics after an injury in water.
Why it matters in the exam
The exam shows a patient with hypopigmented anaesthetic patches and thickened peripheral nerves (leprosy), an aquarium cleaner with a papule on a finger followed by a chain of nodules up the forearm (M. marinum — "fish tank granuloma"), or a large painless ulcer with undermined edges in a patient from Africa (M. ulcerans). The question tests the leprosy spectrum — tuberculoid with strong cell-mediated immunity and few bacilli, versus lepromatous with many bacilli — WHO multidrug therapy (rifampicin, dapsone and clofazimine for 6 months in paucibacillary and 12 months in multibacillary disease), and immune reactions during treatment: reversal reaction and erythema nodosum leprosum (ENL), treated with steroids or thalidomide. Remember that a small number of leprosy cases are diagnosed in Israel, mainly in immigrants, that the disease is notifiable, that it is barely contagious after treatment starts, and that loss of sensation leads to preventable wounds and deformities. In M. marinum, biopsy and culture at low temperature are the key.
Key points
- Mycobacteria cause chronic skin infections that do not respond to routine antibiotics.
- In leprosy the severity is set by the immune response: tuberculoid with few bacilli and lepromatous with many.
- Leprosy is treated with rifampicin, dapsone and clofazimine for 6 or 12 months by classification.
- Leprosy reactions are treated with steroids or thalidomide without stopping treatment.
- M. marinum causes a chain of nodules after an injury in water and is diagnosed by culture at low temperature.
Summary table
| Entity | Clinical picture | Diagnosis | Treatment |
|---|---|---|---|
| Tuberculoid leprosy (paucibacillary) | Few hypopigmented anaesthetic patches, a thickened nerve | Biopsy with granulomas and few bacilli | Rifampicin, dapsone and clofazimine for 6 months |
| Lepromatous leprosy (multibacillary) | Many symmetric lesions, facial thickening, loss of eyebrows | Skin smear with many bacilli | Rifampicin, dapsone and clofazimine for 12 months |
| Leprosy reactions | Reversal reaction: swelling lesions and neuritis; ENL: painful nodules with fever | Clinical diagnosis | Steroids for neuritis; thalidomide for ENL; do not stop treatment |
| M. marinum | Papule on the back of a hand or finger followed by a chain of nodules along the lymphatics (sporotrichoid) | Biopsy and culture at 30–32 degrees | Clarithromycin with ethambutol for months |
| M. ulcerans and rapidly growing mycobacteria | Large painless ulcer (Buruli); infection after cosmetic procedures | Biopsy, PCR and culture | Rifampicin with clarithromycin; surgical debridement |
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Sources
- WHO guidelines for the diagnosis, treatment and prevention of leprosy, 2018 — Multidrug therapy
- ATS/ERS/ESCMID/IDSA clinical practice guideline on nontuberculous mycobacterial disease, 2020 — Skin and soft tissue infection
- Fitzpatrick's Dermatology, 9th edition (2019) — Leprosy and other mycobacterial infections
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.