Updated: 9/19/2020

Mycobacterium leprae

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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
  • Medical 
    • dapsone and rifampin
      • indication
        • tuberculoid and lepromatous types
    • clofazimine
      • indication
        • added therapy for lepromatous types
Complicatons
  • Permanent nerve impairment
  • Deformities

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Questions (4)
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(M1.MC.15.75) A 29-year-old man who recently emigrated from South America presents complaining of a patch of numbness on his skin. He reports that the area has appeared paler than the surrounding skin for a long time. He also has had several cuts and burns near the area, but has no recollection of when the injuries took place and did not feel any pain at the time. On physical exam, you palpate an enlarged ulnar nerve at the elbow. Relevant additional findings from your physical exam are shown in Figure A. You order a biopsy from the edge of the lesion (Figure B). Which of the following most likely caused his disease?

QID: 106735
FIGURES:
1

Sarcoidosis

11%

(6/56)

2

Mycobacterial infection

57%

(32/56)

3

Sporothrix schenckii

21%

(12/56)

4

Contact dermatitis

2%

(1/56)

5

Poxvirus infection

7%

(4/56)

M 2 D

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Evidence (6)
EXPERT COMMENTS (9)
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