tuberculoid leprosy

Definition: The tuberculoid leprosy is a form of leprosy. It is characterized by one or more hypopigmented skin macules and anaesthetic patches, where skin sensations are lost because of damaged peripheral nerves that have been attacked by the human host’s immune cells. Lepromin test is positive. Immune target is the bacillus (Th1 response).

Images

 Tuberculoid leprosy with positive bacilli

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Clinical synopsis

In tuberculoid leprosy, skin lesions are few. One erythematous large plaque is usually present, with well-defined borders that are elevated and that slope down into an atrophic center. The lesions can become arciform or annular.

They can be found on the face, limbs, or elsewhere, but they spare intertriginous areas and the scalp. Lesions can be dry and scaly, hypohidrotic, and hairless.

Another presentation involves a large, asymmetric hypopigmented macule. Both types of lesions are anesthetic and involve alopecia.

Spontaneous resolution can occur in a few years, leaving pigmentary disturbances or scars. Progression can also occur, leading to borderline-type leprosy. In rare instances in which a patient is untreated for many years, the lepromatous type can develop.

The tuberculoid leprosy begins with localized skin lesions that are at first flat and red but enlarge and develop irregular shapes with indurated, elevated, hyperpigmented margins and depressed pale centers (central healing).

Neural involvement is common in persons with tuberculoid leprosy; it leads to tender, thickened nerves with subsequent loss of function. The great auricular, common peroneal, ulnar, and radial cutaneous and posterior tibial nerves are often prominent. Nerve damage can happen early, resulting in wrist drop or foot drop.

Neuronal involvement dominates tuberculoid leprosy. Nerves become enclosed within granulomatous inflammatory reactions and, if small enough (e.g., the peripheral twigs), are destroyed.

Nerve degeneration causes skin anesthesias and skin and muscle atrophy that render the patient liable to trauma of the affected parts, with the development of indolent skin ulcers.

Contractures, paralyses, and autoamputation of fingers or toes may ensue. Facial nerve involvement can lead to paralysis of the eyelids, with keratitis and corneal ulcerations.

Microscopy

In the tuberculoid form of leprosy, well-developed epithelioid granulomas are observed in the papillary dermis, often around neurovascular structures.

The granulomas are surrounded by lymphocytes, which extend into the epidermis. Langhans giant cells are common.

Dermal nerves are destroyed or swollen because of the granulomas. Acid-fast bacilli are not observed.

S-100 is useful in identifying nerve fragmentation and differentiating it from other granulomatous disease.

On microscopic examination, all sites of involvement disclose granulomatous lesions closely resembling those found in tuberculosis, and bacilli are almost never found.

The presence of granulomas and absence of bacteria reflect strong T-cell immunity.

Prognosis

Because leprosy pursues an extremely slow course, spanning decades, most patients die with leprosy rather than of it.

See also

 leprosy

• lepromatous leprosy
• borderline leprosy

Links

 The Raoul Follereau foundation