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Etiology and Pathology

Klebsiella rhinoscleromatis is a gram-negative bacillus closely related to Klebsiella pneumoniae or Friedlander's bacillus (the two can be distinguished by their growth patterns as well as their reactions in bile-containing media). The bacteria can be found in the hard fibrotic nodules in the nose or scattered throughout the submucosa and mucosa in the lesions of the respiratory tract. K. rhinoscleromatis (also previously known as the encapsulated diplococcus of Frisch) is 2-3 micra long and grows aerobically on blood agar or MacConkey's media. It has a low order of pathogenicity for laboratory animals except for mice, and indeed scleroma is only minimally contagious for humans. However, the spread of scleroma is augmented by prolonged contact with infected persons living in crowded quarters. Members of the same family are occasionally affected.

Scleroma most commonly affects the nose, but the nasopharynx, larynx, trachea and bronchi may also be involved. The lesion begins as a submucosal infiltration of neutrophils followed by macrophages and lymphocytes. There is thickening in the nose, paranasal sinuses, or nasopharynx. The initial lesions are soft, red and nonulcerated and form large polypoid masses. Later there is ulceration, crusting, and a discharge. Eventually, fibrosis ensues and the granuloma becomes pale, firm, and pitted. Within the scarred areas, new granulomatous infiltrations may occasionally develop.

The lesions of scleroma spread around and between bone, cartilage and muscle, which may be left behind as isolated islands. Spread may occur via the paranasal sinuses to the upper lip and the alveolar process of the maxilla, and may involve the pharynx by direct extension from the nose. Rarely, scleroma may invade the brain through the cribriform plate and produce a tumor-like lesion at the base of the brain. The nasal septum and the alveolar process of the maxilla may show localized destruction. Cervical lymph nodes may be enlarged.

Histologically, the characteristic granulomatous lesion of scleroma is characterized by masses of lymphocytes, plasma cells, free-lying Russell bodies, and large, foamy macrophages (Mikulicz cells) (Fig. 38.1). The overlying respiratory mucosa undergoes squamous metaplasia with occasional foci of pseudoepithelial hyperplasia, which can be confused with squamous cell carcinoma. This is sometimes followed by atrophy; ulceration tends to be minimal and may result from treatment rather than the infection. After many years, the cellular elements are replaced by dense fibrous tissue, which produces a woody hardness clinically and gives the disease the name scleroma.

The most characteristic histological feature is the Mikulicz cell, which measures 100-200 µm, is vacuolated, non-lipid, and contains the phagocytized causal organisms. The number of these cells varies with the stage of the disease, being most numerous in the nodular stage. Russell bodies are smaller than Mikulicz cells and are plasma cells swollen with globulins. Russell bodies and Mikulicz cells are not pathognomonic for scleroma, and other infections and even neoplasms must be differentiated.

Fig. 38.1 Classical microscopic features of advanced scleroma. There are numerous characteristic foamy macrophages (Mikulicz cells) containing abundant cytoplasm and a uniform, small hyperchromatic nucleus. The inflammatory cell infiltrate is composed chiefly of plasma cells and lymphocytes. X112. AFIP 76664. (From C.H. Binford and D.H. Connor (eds);Pathology of Tropical and Extraordinary Diseases. Washington, D.C., Armed Forces Institute of Pathology, 1976).

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