Mycobacterium leprae

Snapshot

A 35-year-old man presents to the dermatology clinic for a rash. He reports that these spots have been on his skin for about 2 months now since he returned from a work-stay program in South America. There he interacted with animals and occasionally tried exotic foods, such as the armadillo. On physical exam, there are multiple well-circumscribed erythematous plaques with raised borders and central hypopigmentation. There is loss of sensation over the plaques. He is started on a long course of antibiotics.

Introduction

Classification
- Mycobacterium leprae
  - a non-motile, acid-fast bacillus
  - prefers cool temperatures
- transmission
  - respiratory via nasal mucosa
  - via armadillo reservoirs
Epidemiology
- incidence
  - more common in Southeast Asia and South America
- location
  - affects skin and peripheral nerves
- risk factors
  - travel to endemic countries
  - contact with others with leprosy
  - contact with or consumption of reservoirs such as armadillos
Pathogenesis
- the bacteria grows in cool regions, such as the skin and peripheral nerves
- infects macrophages, Schwann cells, and keratinocytes
- lepromatous Hansen disease
  - weak cell-mediated immunity
  - humoral Th2-type immune response
  - high burden of bacteria in lesions
- tuberculoid Hansen disease
  - strong cell-mediated immunity
  - Th1-type immune response
  - low burden of bacteria in lesions
Associated conditions
- lepromatous Hansen disease
- tuberculoid Hansen disease
- erythema nodosum
Prognosis
- slow progression that may develop over months or years
- may have intermittent acute leprosy reactions
lepromatous type is more severe

Presentation

Symptoms
- lepromatous Hansen disease
  - diffuse rash
- tuberculoid Hansen disease
  - multiple discrete lesions
Physical exam
- patients often present with overlapping findings
- peripheral neuropathy
  - foot drop
  - facial nerve palsy
  - contractures or hand or feet
  - loss of sensation
- lepromatous Hansen disease
  - leonine facies (lion-like)
    - thickened foreheard, ears, eyebrows, and cheeks
  - diffuse plaques and nodular skin lesions symmetrically distributed
    - may be erythematous or hypopigmented without sharp borders
- tuberculoid Hansen disease
  - multiple discrete erythematous plaques with central hypopigmentation and raised discrete borders
    - plaques often have loss of sensation
    - hairless
dry with some scale

Studies

Labs
- tissue polymerase chain reaction (PCR)
- may test as falsely positive on VDRL testing
Biopsy or slit-skin smear
- acid-fast bacilli
- granulomas
Making the diagnosis
based on clinical presentation and tissue diagnosis

Differential

Morphea
- distinguishing factor
  - also presents with thickened skin but usually does not involve peripheral nerve damage
Vitiligo
- distinguishing factor
also presents with hypopigmentation but without peripheral nerve damage or raised borders

Treatment

Complicatons