Skin nontumor

Infectious disorders


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PubMed Search: Leprosy infection [title]

Mowafak Hamodat, M.B.Ch.B., M.Sc.
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Cite this page: Hamodat M. Leprosy. website. Accessed September 29th, 2023.
Definition / general
  • Also called Hansen disease
  • Most U.S. cases occur in immigrants
  • Worldwide distribution due to travel and migration but endemic in tropics
Clinical features
  • Mycobacterium leprae is an obligate intracellular gram positive and weakly acid fast organism
  • The complexity of presentation is related to the varied immunologic responses
  • The incubation period is usually 3 - 5 years
  • Tuberculoid leprosy occurs in individuals with good cell mediated immunity; patients develop granulomatous response
  • Lepromatous leprosy occurs in individuals with poor cell mediated immunity; do not develop a granulomatous response
  • Borderline leprosy is an intermediate form between tuberculoid and lepromatous leprosy
  • Transmitted by nasal discharge and digital impregnation of skin, as bacilli can be carried under nails and are inoculated under the skin by scratching
  • Lucio phenomenon is seen in Mexican and Central American patients who present with untreated, diffuse, non nodular lepromatous leprosy with hemorrhagic infarct
  • Planter lesions are at increased risk to develop squamous cell carcinoma (Indian J Lepr 1998;70:179)
  • Diagnosis is by PCR; most skin lesions have no identifiable bacteria (J Lab Physicians 2011;3:21)
  • Mitsuda reaction: intradermal injection of an armadilloderived lepra bacilli, is useful for classification

  • Description:
    • Tuberculoid leprosy has hypopigmented center and raised erythematous border
    • Lepromatous leprosy has macules, papules and plaques, but firm nodules may also be seen in the face
    • Borderline leprosy has hypopigmented macules
  • 16S ribosomal RNA gene PCR assay (can use paraffin block)
Case reports
  • Clarithromycin, rifampin and dapsone
Microscopic (histologic) description
  • Tuberculoid leprosy: epithelioid histiocytes surround small cutaneous nerves; Langhans giant cells may be seen but without necrosis; the infiltrate may involve the papillary dermis up to the epidermis; may destroy arrectores pilorum muscle; bacilli are usually scarce
  • Lepromatous leprosy: macrophages (Virchow cells, lepra) are found in poorly circumscribed masses in the dermis, with few / no lymphocytes; macrophages may be distended with large groups of leprosy bacilli (globi); bacteria are present in large numbers in cutaneous nerves and in endothelium and media of small and large vessels; may invade arrectores pilorum muscle; may have subcutaneous nodules (erythema nodosum leprorum)
  • Borderline leprosy: perineural fibrosis with lamellar or onion skin pattern; more circumscription of the granulomatous response, more lymphocytes and closer relationship to nerves
  • Indeterminate leprosy: scanty superficial and deep lymphohistiocytic infiltrate in the dermis with some tendency to localize around appendages; increased mast cells
  • Histiocytoid leprosy: spindle cell proliferation with storiform pattern suggestive of fibrous histiocytoma
  • Lucio phenomenon: leukocytoclastic vasculitis and epidermal infarction
Microscopic (histologic) images

Contributed by Mowafak Hamodat, M.Sc.

Lepromatous leprosy

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Lepromatous leprosy, low magnification

Mycobacterium lepromatosis infection

Positive stains
Differential diagnosis
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