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Updated: Sep 19 2020

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
    • 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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