• Clinical science

Leprosy (Hansen disease)


Leprosy (Hansen disease) is a chronic infectious disease caused by prolonged exposure to Mycobacterium leprae, an acid-fast, slow-growing, fastidious bacillus. Leprosy primarily occurs in tropical and/or developing countries and is rarely observed in the US. There are various forms whose descriptions differ among two different classification systems, but the three cardinal clinical manifestations of leprosy are hypopigmented skin lesions, nerve thickening, and peripheral nerve palsies. Long-standing cases of leprosy classically develop deformities as a result of contractures following motor nerve palsies and/or repeated injury due to sensory loss. Other chronic complications include uveitis, orchitis, and nasal septal perforation. Patients with leprosy may also present with acute lepra reactions that are characterized by painful skin lesions and neuritis. The diagnosis is usually confirmed with the help of a biopsy. Lepromin tests aid in the classification of various forms of leprosy. Treatment consists of prolonged MDT (multi-drug therapy) with dapsone and rifampin. Clofazimine is added to the therapeutic regimen in patients with multibacillary leprosy.


  • US statistics
    • Incidence: 100–200 new cases annually
    • Prevalence: ∼ 4,000 cases in total
  • Sex: >
  • Peak incidence: 10–20 years
  • Endemic to tropical regions: India, Brazil, Indonesia, Nepal, Myanmar, Nigeria

Epidemiological data refers to the US, unless otherwise specified.


  • Pathogen: Mycobacterium leprae is an obligate, intracellular, acid-fast bacilli that cannot be cultured.
  • Route of transmission
    • Respiratory droplet transmission
    • Close contact with fomites, infected soil, and/or infected individuals
    • Transmission usually requires prolonged exposure, and some individuals seem more predisposed than others
  • Infectious type: multibacillary leprosy (see “Pathophysiology” below)
  • Reservoirs: infected humans; , nine-banded armadillos


Lepromatous leprosy (LL) Tuberculoid leprosy (TT)
  • Th2 response
    • Reciprocal inhibition of Th1 response →inadequate cell-mediated immune response → many lepra bacilli
    • Antibody production (hypergammaglobulinemia);
  • Nerve lesions are the result of M. leprae invasion.
  • M. leprae grows best at cool sites in the body (skin, mucous membranes, peripheral nerves, anterior chamber of the eye, upper respiratory tract, testes).
  • ↑ Th1 response
    • Strong cell-mediated immune responsegranuloma with epitheloid cells and lymphocytes but few or no lepra bacilli
  • Nerve demyelination is the result of a T-cell mediated response.

Leprosy is a slowly progressive, chronic infection with a spectrum of clinical manifestations depending on the degree of cell immunity.

Clinical features

  • Incubation period: 3–5 years
  • The clinical manifestations vary depending on the type of leprosy (LL, TT, or intermediate forms collectively known as Borderline leprosy, which is explained in further detail in extra information)
Lepromatous leprosy (LL) Tuberculoid leprosy (TT)
Cutaneous manifestations
  • Multiple symmetrical macules, plaques, and/or nodules
    • Nodules in the face may coalesce → leonine facies
    • Nodules may ulcerate
  • Hypesthesia of the skin lesion is less common and occurs only in late stages of the disease
  • Supraciliary and ciliary madarosis
  • Few (usually 1–3 lesions), localized, hypopigmented macules, plaques, and/or papules with well-defined, erythematous, and/or raised margins
  • Lesions are dry, scaly, anhidrotic
  • Hair loss
  • Hypesthesia of the skin lesion is common and occurs early.
Nerve involvement*
  • Occurs late but is more extensive
  • Acral, distal, symmetrical anesthesia
  • Usually begins as a “glove and stocking” neuropathy that spreads proximally
  • Occurs early but is localized
  • Asymmetric enlargement of one or many peripheral nerves
  • Acute neuritis does not occur.
Systemic manifestations
  • Not involved
  • *Nerve involvement leads to nerve enlargement and peripheral nerve palsies which present with sensory, motor, and/or autonomic deficits.

The three cardinal clinical manifestations of leprosy are hypopigmented skin lesions, nerve thickening, and peripheral nerve palsies!

All peripheral nerves can become affected in leprosy, but the most commonly affected are the ulnar and the peroneal nerves.


Lepromatous leprosy (LL) Tuberculoid leprosy (TT)
Skin scraping or slit-skin smear findings*
  • Smears are positive for AFB at any one location
  • Smears are negative for AFB at all locations
Biopsy findings**
  • Granulomas formed by epithelioid cells and Langerhans giant cells
  • Many lymphocytes with a a CD4::CD8 ratio of 1.2:1
Lepromin test*** - +++
  • *Modified Ziehl-Neelsen staining of scrapings from skin lesions, nasal swabs, and/or slit skin smears from ear lobes are used to screen for leprosy.
      • BI is primarily used to classify leprosy
  • **Punch biopsy followed by histopathological examination with modified Ziehl-Neelsen staining is used to confirm the diagnosis.
  • ***Lepromin test:
    • Antigen is injected intradermally on the ventral forearm
    • The test is positive if induration is > 5 mm
    • Measures the ability of a patient to mount a T cell response. Does not diagnose leprosy.
      • Can be positive in patients with no exposure or infection to leprosy
      • Can distinguish between lepromatous leprosy (negative result due to inadequate cell-mediated response) and tuberculoid leprosy (positive result due to strong cell-mediated immune response).

Diffuse hypergammaglobulinemia associated with lepromatous leprosy can cause false positive VDRL, RF, and/or ANA tests and thus result in diagnostic confusion!


  • Definitive therapy: Multidrug therapy [1]
Lepromatous leprosy (LL) Tuberculoid leprosy (TT)
Treatment duration 12 months 6 months
Clofazimine x
  • Supportive therapy
    • Treatment of lepra reactions (see “Complications” below)
    • Rehabilitation
      • Physiotherapy to prevent contractures
      • Surgery to correct deformities (e.g., tendon transfer surgery for ulnar nerve palsy)
    • Wound care


  • Secondary deformities
    • Bone destruction → shortened digits, autoamputation
    • Neuropathic ulcers on the dorsum of the foot
    • Charcot joints
  • Nose: saddle nose deformity, anosmia, septal perforation
  • Eye
    • Lagophthalmos and corneal insensitivity → corneal ulcers
    • Invasion of the anterior chamber → chronic uveitis → blindness
  • Orchitistesticular atrophyhypergonadotropic hypogonadism
  • Reactive amyloidosis
  • Lepra reactions (see extra information for more details)

Patients may attribute lepra reactions to side effects of medications and stop them. Therefore, they should be warned about possible lepra reactions and told to seek treatment as soon as they occur. Treatment of leprosy should not be stopped when lepra reactions occur.

The presence of tender nerves in a patient with leprosy indicates a lepra reaction!

We list the most important complications. The selection is not exhaustive.

last updated 01/08/2019
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