7.1.2.3 Leprosy

Leprosy is a chronic granulomatous infection caused by M. leprae, an acid-fast bacillus. The disease is characterized by lesions in skin, mucous membranes, nerves, and eyes. The ocular lesions include keratitis, uveitis, scleritis, and episcleritis. M. leprae was Þrst recognized by Hansen in 1874 but to date has never been cultured in vitro and requires a host, such as the human, or experimental animals, such as the mouse (foot pads), for propagation [52]. M. leprae infections are very uncommon in western societies but have signiÞcant prevalence in central Africa, the Middle East, and Southeast Asia, including India and Indonesia, and some countries of temperate climate, such as North and South Korea, Argentina,andCentralMexico[53].Susceptibility to M. leprae varies according to the sex, race, and geographic distribution of the involved population [54]. According to the Madrid classiÞcation, there are three clinical forms of the disease, depending on the immune response of the host: tuberculoid, borderline, and lepromatous [55]. Patients with tuberculoid leprosy exhibit only a few discrete demarcated, hypopigmented, and hypoesthetic skin lesions that histologically consist of granulomas, resembling those of tuberculosis, and a few acid-fast bacilli. The dermal nerves also are involved, usually in a symmetrical pattern. Patients with lepromatous leprosy exhibit multiple diffuse skin lesions and peripheral nerve involvement. Cell-mediated immunity is impaired in these patients [56]. Histologically, the lesions contain many macrophages and histiocytes with many intracellular, extracellular, and intravascular acid-fast bacilli. Thickening of the facial skin leads to the characteristic leonine facies. Eye involvement is more common in this type of leprosy than in the tuberculoid form [57]. Borderline leprosy shares characteristics of tuberculoid and lepromatous types of leprosy.

Scleritis, episcleritis, and anterior uveitis are the initial manifestations in up to 16% of leprosy patients [58] and are more commonly seen in lepromatous leprosy than in tuberculoid leprosy. Scleritis and episcleritis in leprosy may be initiated by a direct M. leprae invasion, but an immunemediated reaction to the products from the

destroyed bacilli may also produce inßammation. The episcleritis may be simple or nodular. The scleritis is usually nodular, but it may progress to necrotizing scleritis. Direct M. leprae scleral invasion usually arises de novo although it may result as an extension of lesions in adjacent tissues, such as lids or uveal tract. Scleritis is characterized by miliary lepromas with macrophages and M. leprae, is usually bilateral, and often is accompanied by mucopurulent discharge. Scleritis is usually recurrent over many years, with exacerbations lasting 3Ð4 weeks. Chronic or recurrent scleritis in leprosy may lead to scleral thinning and staphyloma formation.

M. leprae bacilli migrate from sclera into the cornea, causing superÞcial avascular keratitis characterized by whitish, subepithelial corneal opacities that usually begin in the superior or supratemporal quadrant and spread from peripheral to central areas; corneal opacities eventually coalesce and cause gradual decrease of vision. SuperÞcial neovascularization occurs later in the disease and forms the classic superior or supratemporal leprous pannus. Edematous corneal nerves resembling beads on a string are pathognomonic of leprosy [59]. Corneal invasion from scleral M. leprae bacilli also may cause interstitial keratitis, which usually appears in the superior quadrants as deep stromal inßammation with progressive vascularization [59, 60]. In some cases, interstitial keratitis is secondary to the deeper extension of the superÞcial avascular keratitis. When the inßammation subsides, the vascular ßow diminishes, leaving behind ghost vessels in midto deep stroma. Scleritis also may be associated with anterior uveitis, which is characterized by iris pearls or creamy white particles consisting of bacilli and monocytes [61], by iris atrophy or loss of iris stroma, and by small, nonreactive pupils [62]. Iris pearls are pathognomonic of ocular leprosy. Angle-closure glaucoma may result from seclusion of the pupil by posterior synechiae.

The diagnosis of leprous scleritis is made on the basis of clinical and histopathological Þndings. Dermatological and ocular Þndings substantiate the diagnosis, which is conÞrmed by the Þnding of granulomatous inßammation with acid-fast