Closing the Brief Case: Delayed Diagnosis of Cutaneous Mycobacterial Infection in Rural Mississippi

ANSWERS TO SELF-ASSESSMENT QUESTIONS

• 1.What is the stain of choice for M. leprae?
  • a.Ziehl-Neelsen stain
  • b.Fite-Faraco stain
  • c.Kinyoun stain
  • d.Hematoxylin and eosin stain

Answer: b. M. leprae may be negative on routine AFB stains, including Kinyoun and Ziehl-Neelsen stains. Fite-Faraco, a modified acid-fast stain, is the stain of choice.

• 2.How long does M. leprae usually take to grow on routine mycobacterial cultures?
  • a.6 weeks
  • b.8 weeks
  • c.12 weeks
  • d.Does not grow on routine mycobacterial cultures

Answer: d. Failure to grow on culture, including on media optimized for mycobacterial pathogens, is a notable characteristic of M. leprae. The other mycobacterium that does not grow in culture is M. lepromatosis. M. marinum, M. haemophilum, and M. xenopi may require specific conditions to grow on cultures.

• 3.What type of immunologic reaction is a reversal reaction?
• a.Immune complex-mediated reaction
• b.Delayed-type hypersensitivity reaction
• c.Cytotoxic reaction
• d.Immediate hypersensitivity reaction

Answer: b. The type 1 immune reaction, also known as reversal reaction, is a delayed-type hypersensitivity reaction, whereas the type 2 reaction, or ENL, is thought to be an immune complex-mediated reaction.

TAKE HOME POINTS

• •Leprosy is an underdiagnosed disease caused by M. leprae and/or M. lepromatosis. These organisms have the following characteristics:
  • ∘They are Gram-positive, acid-fast, and intracellular.
  • ∘Fite-Faraco is the stain of choice.
  • ∘They fail to grow on routine artificial liquid and solid culture media.

• •Clinical manifestations of leprosy include skin lesions and nerve dysfunction. However, musculoskeletal involvement including inflammatory arthritis, though underreported, is quite common.
• •Leprosy is notable for characteristic immunologic reactions, which include the following:

• ∘Type 1 reaction, or reversal reaction, is a delayed hypersensitivity reaction that most commonly occurs in borderline forms of leprosy with clinical manifestations that include increased erythema, edema of the hands and feet, neuritis, and arthritis.
• ∘Type 2 reaction, or erythema nodosum leprosum, is an immune complex-mediated reaction that occurs most commonly in borderline leprosy or lepromatous leprosy and is usually associated with systemic symptoms and painful subcutaneous nodules.