Rhinoscleroma is a chronic granulomatous bacterial disease of the nasal cavity, but may also affect the upper respiratory tract (nasopharynx, layrnx, trachea, bronchi). It is a tropical disease rarely seen in the United States, and is principally found in Africa and Central America. The causative agent is Klebsiella rhinoscleromatis, a subspecies of Klebsiella pneumoniae (gram-negative bacillus).

Histologically, biopsies they pseudoepitheliomatous hyperplasia, mixed lymphoplasmacytic infiltrates (often with Russell bodies) and Mikulicz cells ("parasitized" vacuolated histiocytes that contain the bacteria).

Inhalation of contaminated droplets is the main mode of infection. The disease has passes through 3 stages: catarrhal, granulomatous, and sclerotic. Initial presentation is similar to an upper respiratory infection with rhinitis (catarrhal stage). However, the disease then progresses to cause a purulent rhinorrhea with thickening of the nasal mucosa and skin, and epistaxis (granulomatous). The sclerotic phase of disease is characterized by destruction of the nasal cartilage.

As there is some evidence that rhinoscleroma tends to affect families, genetic host response may be involved in pathogenesis (de Pontual). This is also supported by the fact that Mikulicz cells are macrophages that demonstrate ineffective phagocytosis.