Definition: Leprosy is a chronic granulomatous infection affecting the cooler parts of the body (Skin, peripheral nerves, nose, anterior chamber of the eyes) caused by Mycobacterium leprae.

It is also known as Hansen’s disease after the scientist who   discoverer the M Leprae

Aetiology: Mycobacterium leprae.- Gram negative intracellular(Macrophage) acid fast bacilli(weak acid fast- by 5% H2SO4).

♦Non-culturable in artificial media

♦But can be grown on mouse foot pad and also in armadillo due to low body    temperature and long life span.

Epidemiology:  2/3 of Leprosy now-a-days in India. Also common in Africa.

Incubation period: 2-5 years.           Generation time: 13 days (average.)

Source: Untreated infectious leprosy patients (Multibacillary type)

Mode of Transmission:  Nasal mucosa (Mainly respiratory route), Others (broken skin lesion),

Route-  Airborne

Nerves usually affected by Leprosy

Ulnar Nerve 2) Median Nerve causing causing claw hand 3) Radial Nerve  causing Wrist drop4) Common peroneal nerve causing Foot drop. 5) Posterior Tibial Nerve  passess Posterior and inferior to the medial malleolus. 6) Great Auricular Nerve 7) Skin Sensory Nerves near skin lesions may be enlarged. 8. 7th Cranial Nerve -It is not palpable but damage to the nerve leads to facial paralysis and lagophthalmos. 9) 5th Cranial Nerve Sensory Fibers -If it is damaged, it leads to anaesthesia of cornea.

Classification of Leprosy

For treatment purpose

1. Paucibacillary leprosy-Slit skin smear negative

2. Multibacillary Leprosy-Slit skin smear Positive

Classification of Leprosy by Ridley and Jopling

1.TT (Tuberculoid Tuberculoid)-Infiltrated plaques,one or few (Upto 5 lesions),often hypopigmented,Localized,asymmetrical,well defined with sharp borders,sensation absent,bacilli not detected

2.BT (Borderline Tuberculoid)-Infiltrated plaques,single usually with satelite lesions or more than 5 lesions,not diffuse and asymmetrical distribution,border welldefined and sharp,sensation absent,bacilli few(1+),if any detected.

3.BB (Borderline Borderline) -Plaque and domed shaped punched out lesions,many but asymmetrical distribution,poorly defined border,sensation diminished,bacilli many in lesions.

4. BL(Boderline Lepromatous)-Macules,plaques,papules,infiltration,lesions are many that tendency to symmetrical distribution,less welldefined border,sensation diminished.Many bacilli in skin lesions.

5.LL (Lepromatous Leprosy)-Macules,papules,nodules,diffuse infiltration,neumerous,symmetrical,difficult to distinguish between normal and affected skin,sensation not affected,numerous bacilli(Globi)in skin lesions.

Indeterminate leprosy

Often the first lesion noted is a solitary, ill-defined, hypopigmented macule that merges into the surrounding normal skin. Less often, erythematous macules may be present. Such lesions are most likely to occur on the cheeks, upper arms, thighs, and buttocks. Examination reveals that sensory functions are either normal or minimally altered. Peripheral nerves are not enlarged, and plaques and nodules do not occur. Histologically, a variable lymphocytic infiltrate (without granulomas) is seen, sometimes with involvement of the cutaneous nerves. Usually, no bacilli, or only a few, are seen on biopsy of this indeterminate form.

Reactional States: 50% of Leprosy patients will experience a reaction after antibiotic treatment.Type I Lepra Reactions (upgrade)-Type IV hypersensitivity – Cell-mediated change Type II lepra reaction Erythema Nodosum Leprosum ( Immune complex reaction (type III) between M. leprae antigens and host.Type III Lepra Reaction /Lucio Phenomenon-Due to deep cutaneous vasculitis

Diagnosis of Leprosy:

Typical Leprotic patch

Isolation of organism (Slit Skin Smear +)

Enlargement of peripheral nerves

If any of the two found as positive the  diagnosis of Leprosy is confirmed.

Typical Leprotic patch: 4H

1.Hyposthetic, 2.hypopigmented,3.hypohydrotic,4.hypotrichotic patch


1. SSS- Slit Skin Smear: Stained with modified ZN –stain microscopic examination of Leprosy bacilli

MI (morphological index): is the index of living bacteria, Significance of it is early detection of efficacy of treatment.(Dapsone resistance)

BI(Bacterial Index): is index of density of leprosy bacilli (both living&death) Significance of it is diagnostic, and prognostic.

2.Skin biopsy for histopathological examination


Treatment of Leprosy

For Indeterminate leprosy : ROM therapy; Single dose

Rifampicin 600mg + Ofloxacin 400mg + Minocycline 100mg

For Paucibacillary cases (I, TT, BT)                for remember;  DR therapy

1. Dapsone100 mg   daily  6 months 

2. Rifampin 600mg  monthly for 6 months 

For Multibacillary cases (LL,BL,BB)            for remember DCR therapy

1. Dapsone100 mg   daily

2. Clofazimine 50mg  daily &  150mg monthly

3.Rifampin 600mg  monthly

for 1-2 years or till smear negative