[New aspects in the histopathology of infectious skin diseases]

An infectious pathogenesis should always be considered in inflammatory infiltrates in the skin. While some organisms can be recognized on hematoxylin-eosin staining (e.g. yeasts, leishmania), histochemical and immunohistochemical stainings are available for others.

If no organisms are seen in a section, the diagnosis of an infection cannot be made with surety, but the pattern of the inflammatory infiltrate can still be suggestive of an infectious process. New or little-known reaction patterns and difficulties in differential diagnosis will be demonstrated.

Selective literature review and analysis of individual cases.

Studies using molecular techniques to identify organisms in biopsy specimens have helped to better characterize the histomorphological spectrum of skin infiltrates in infectious skin diseases. Apart from unusual herpes simplex and varicella zoster infections, the histopathology of coxsackie virus and measles exanthem, borreliosis, syphilis, and of cutaneous leishmaniasis is demonstrated. For numerous organisms, molecular tests have been established that can be used on the formalin-fixed, paraffin-embedded material.

Selected skin infections demonstrate the broad histomorphological spectrum of skin infiltrates induced by infectious organisms. It is important for histopathologists to know which reaction pattern requires them to alert the clinician to necessary ancillary diagnostics (culture, serology) and when to consider molecular diagnostics to be performed on the biopsy specimen.