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Lepromatous Leprosy

This pattern develops when there is a reduced cell-mediated response. The histological lesion is the leproma, which comprises many closely packed histiocytes, each containing enormous numbers of bacilli. There is no surrounding lymphocytic response and no granuloma formation; the cellular infiltrate does not extend up to the epidermis but leaves a characteristic clear zone free from bacilli. There are numerous bacilli in the Schwann cells and there is marked edema within the nerve sheath, but no cellular reaction (Fig. 34.3 D).

Unlike tuberculoid leprosy, the disease is not localized and spreads rapidly, both locally and by bloodborne dissemination which affects other parts of the skin, the nerves, the mucosa of the upper respiratory tract (especially the paranasal sinuses), and all the organs of the body, particularly the eyes, testes, bone marrow of the phalanges, and (to a lesser extent) superficial muscle, liver, lymph nodes, and spleen. The very multiplicity of lesions is characteristic. There is no anesthesia, but skin infiltration and nodulation occur. Many bacilli will be found in the nasal and sinus mucosa; the larynx and bronchi are both affected, a feature more commonly seen in Asia than in Africa.

Damage to the nerves follows slowly, and is usually symmetrical. It is due to multiplication of the bacilli in the Schwann cells. Sensation is lost eventually, and over many years results in anesthesia of the limbs and even much of the trunk. Motor damage may occur, but tendon reflexes remain intact until late in the disease.

Lepromatous leprosy is therefore a systemic disease with multiple organ involvement. Bones may be directly invaded in lepromatous leprosy, particularly the nasal bones, the phalanges and the alveolar process of the maxillae. The nasal cartilage is commonly invaded, the septum ulcerates, and the bridge of the nose may collapse.

The organ most affected is the testis, with invasion of the seminiferous tubules causing sterility. It is probable that gynecomastia which occurs in lepromatous leprosy results primarily from damage to the Leydig cells of the testes, with liver damage and protein malnutrition contributing. The eye is affected by hematogenous spread; and lepromata may be seen on the conjunctiva; keratitis and iritis occur. Damage to the fifth and the seventh nerves occurs early; other cranial nerves are unaffected.

All the lymph nodes, both beneath the skin and deeper, may be affected; smooth and striated muscles are also invaded and in some cases wasting of the face, hands, and feet is due to muscle invasion rather than major nerve involvement. (It is particularly difficult to clear the M. leprae from muscles by treatment.) Liver damage can be severe and the kidneys and spleen may also be affected.

Acid-fast bacilli are present in all lesions in lepromatous leprosy; smears are consistently positive and the lepromin test is negative.

Lucio leprosy is a name given to a diffuse, highly anergic form of lepromatous leprosy found in South and Central America, but particularly in Mexico in patients of Latin American origin. Clinically it may be so diffuse that it is difficult to detect unless there is loss of body hair, such as in the eyebrows. In the later stages there is obstructive vasculitis in the small cutaneous vessels (see Fig. 34.3F), which can result in ulceration because of dermal infarcts. Opportunistic infections can result in septicemia, which can be fatal.

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Fig. 34.3 A-F. Facial changes in lepromatous leprosy. A There is diffuse infiltration with a few papules over the central part of the face, and there are nodules on the ear lobes. AFIP 93-5684. (From Meyers 1995) B, C More advanced lepromatous leprosy. Both patients show nodular infiltration, loss of eyebrows, and thickening of the ear lobes. The appearance in C has been described as "leonine" and is characteristic of advanced lepromatous leprosy. The patients in B and C are both African males. D Polar lepromatous leprosy. Except for a well-defined subepidermal clear zone (grenz), the dermis is expanded and in part replaced by foamy histiocytes and only a few lymphocytes. H&E, x220; AFIP 65-1653. (From Meyers 1995) E Subpolar lepromatous leprosy, showing lamellar thickening of the perineurium and large numbers of acid-fast bacilli in the nerve and surrounding histiocytic infiltration. Fite-Faraco, x504; AFIP 73-7532. (From Meyers 1995) F Lucio leprosy. Endothelial cell proliferation nearly completely obstructs the lumen of a dermal blood vessel. Acid-fast bacilli colonize the endothelial cells. Fite-Faraco, x630; AFIP 57-9794-1. (From Meyers 1995).

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