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Skin-nontumor / Clinical Dermatology

Infectious disorders


Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC (see Reviewers page)
Revised: 5 September 2011, last major update March 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● Chronic cutaneous infection caused by Mycobacterium leprae


● Also called Hansen’s disease


● Most US 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 armadillo–derived lepra bacilli, is useful for classification

Clinical 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

Micro description

● Tuberculoid leprosy: epithelioid histiocytes surround small cutaneous nerves; Langerhans 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

Micro images

Various images


Lepromatous leprosy images contributed by Dr. Mowafak Hamodat

Positive stains

● Modified Ziehl-Neelsen stain (Wade-Fite) stain

Virtual slides

Lepromatous leprosy

Differential diagnosis

● Fibrous histiocytoma

End of Skin-nontumor / Clinical Dermatology > Infectious disorders > Leprosy

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