bubble_chart Overview

Leprosy is a contagious disease caused by Mycobacterium leprae, primarily affecting the skin, mucous membranes, and peripheral nerves, and can also involve deep tissues and organs. Mycobacterium leprae mainly enters the human body through broken skin and mucous membranes. This disease is not congenital nor hereditary.

bubble_chart Epidemiology

(1)、Source of infection

Leprosy patients are the only source of infection for this disease, with lepromatous and borderline cases being the most infectious.

(2)、Transmission routes

Mycobacterium leprae primarily enters the human body through broken skin and the respiratory tract.

(3)、Population susceptibility

Human susceptibility to Mycobacterium leprae varies significantly. Generally, children are more susceptible than adults, yet most cases occur in individuals over 20 years old, with male cases outnumbering female cases.

bubble_chart Etiology

Etiology

The leprosy bacillus belongs to the genus Mycobacterium, with short rod-shaped or slightly curved bacterial bodies measuring approximately 2-6 μm in length and 0.2-0.6 μm in width. It appears red under acid-fast staining and is Gram-positive. The leprosy bacillus can survive for 3-4 weeks at 0°C, loses its reproductive capacity after 2-3 hours of strong sunlight exposure, and can be inactivated by boiling for 8 minutes.

bubble_chart Clinical Manifestations

Leprosy is classified into five types according to the five-tier classification system: tuberculoid leprosy (TT), borderline tuberculoid leprosy (BT), mid-borderline leprosy (BB), borderline lepromatous leprosy (BL), and lepromatous leprosy (LL). The early stage of all types of leprosy is indeterminate leprosy (I).

1. Tuberculoid leprosy (TT)

   This type is relatively common clinically, with lesions often confined to peripheral nerves and skin. The skin lesions are red macules and papules, or red or dark red patches, round or irregular in shape, with clear edges, dry and hairless surfaces, sometimes with scales. Local sensory impairment appears early and is pronounced.

2. Borderline tuberculoid leprosy (BT)

   Common skin lesions include macules and papules, patches, and infiltrative lesions, with basic characteristics similar to tuberculoid leprosy but with multiple lesions. Typical lesions have a distinct "clear zone" in the center, often surrounded by small satellite lesions. Multiple peripheral nerve lesions are present, and sensory impairment in the skin lesions is pronounced.

3. Mid-borderline leprosy (BB)

   Typical lesions are dual-type lesions of macules and papules with infiltration, presenting with polymorphic and multicolored characteristics. Characteristic saucer-shaped, target-like, or satellite lesions may be seen. Facial lesions resembling a bat are referred to as a "dual-type face." Lesions vary in size and are numerous; nerve lesions are multiple but asymmetrical. The damage and functional impairment of the skin and nerves lie between tuberculoid and lepromatous leprosy. Mid-borderline leprosy can transform into tuberculoid or lepromatous leprosy.

4. Borderline lepromatous leprosy (BL)

   Skin lesions include macules and papules, patches, nodules, and diffuse infiltration, widely distributed and incompletely symmetrical, with few visible lesion edges. Some diffuse infiltrations may have a clear central zone. Superficial nerves are enlarged, multiple but asymmetrical. In advanced-stage patients, lesions may merge into large areas, and deep facial infiltration can form a "leonine face," with nasal septum ulcers or saddle nose. The disease can also invade internal organs.

5. Lepromatous leprosy (LL)

   Early-stage lepromatous lesions are mostly macules and papules, pale red or light-colored, with blurred edges, small but numerous, and symmetrically distributed. There is no obvious sensory impairment or anhidrosis, but abnormal sensations such as itching or crawling may occur. Long-term cases may show delayed temperature and pain sensation.

   Intermediate-stage [second stage] lepromatous leprosy may present with macules and papules, diffuse infiltration, and nodules, with unclear edges, shiny and juicy surfaces, widely distributed, and possible grade I superficial sensory impairment locally.

   Advanced-stage lepromatous leprosy shows more pronounced diffuse infiltration, extending deeper, with most of the body's skin affected. Facial skin becomes diffusely thickened, with deepened forehead and temple wrinkles, thickened nasolabial folds, and enlarged earlobes. Extensive deep infiltration occurs in the limbs and trunk, with significant sensory impairment and anhidrosis.

   Nerve damage is not obvious in the early stage, with no palpable nerve thickening. In intermediate and advanced stages, widespread and symmetrical nerve trunk thickening may occur, leading to severe deformities and disabilities.

   Early-stage symmetrical thinning of the outer eyebrows occurs. As the disease progresses, eyebrows and eyelashes may all fall out. Hair may also gradually thin.

   Mucous membrane damage appears early and is pronounced. In intermediate and advanced stages, lymph nodes, testes, eyes, and internal organs are often affected.

6. Indeterminate leprosy (I)

   This is the early stage of leprosy, typically presenting with a small number of macules and papules, mostly light-colored, with a few pale red, edges clear or unclear, and varying degrees of superficial sensory impairment.

7. Leprosy reaction

   During the chronic course of leprosy, patients may suddenly experience active symptoms, new skin lesions, accompanied by acute or subacute symptoms such as aversion to cold and fever. This allergic phenomenon is called a leprosy reaction.

Involvement of the great auricular nerve can cause thickening and enlargement. The facial nerve may spasm due to lesion invasion and irritation or show peripheral deviation of the mouth due to lesion compression. The coexistence of spasms and deviation of the mouth is characteristic of leprosy-related deviation of the mouth.

bubble_chart Diagnosis

Based on the history of leprosy contact, a chronic sexually transmitted disease course, damage to the skin, mucous membranes, and peripheral nerves throughout the body, and the detection of leprosy bacilli in secretions or biopsies from the affected areas, a definitive diagnosis can be made.

bubble_chart Treatment Measures

Currently, there are safe and effective drugs and methods for treating leprosy. Generally, a combination of chemotherapy drugs such as dapsone, rifampicin, solapsone, and prothionamide is used for leprosy patients, or immunotherapy is employed. For leprosy reactions, treatments like thalidomide and adrenocortical hormones can be used.

bubble_chart Differentiation

Advanced stage leprosy must be differentiated from subcutaneous nodules and syphilis.