Male genital rashes are very common. They may be confusing to identify and are often difficult to treat. Some rashes may occur exclusively on the genitalia; others, which are typically found on other parts of the body, have an atypical appearance when present on the genitalia. The skin over the genitalia is thin and moist, so typical dry scaliness may not be present.
The most common inflammatory reaction affecting the male genitalia is psoriasis. The patient develops bright red, well-defined, scaling plaques. Often the entire scrotum, inguinal folds, and penis are involved. Figure 18-8 shows psoriasis of the penis.
Another form of genital rash is contact dermatitis. It may develop from soaps or disinfectants. Irritants used for facial actinic keratoses may inadvertently be transferred to the genitalia. Itching is a major symptom.
Fixed drug eruptions are unique reactions that appear in the same area of the body each time the responsible drug is given. Fixed drug reactions manifest as a sudden onset of multiple, well-defined, macular, eczematous, bullous patches. When the genitalia are involved, these eruptions typically occur on the distal penis and glans and may be very painful. Antibiotics and laxatives containing phenolphthalein may cause such rashes. Figure 18-9 shows a fixed drug reaction. More than 500 medications have been implicated in fixed drug reactions;therefore, the examiner should take a careful medication history.
Lichen planus is an inflammatory disorder characterized by violaceous, flat, shiny papules ranging from 0.75 to 3 inches (2 to 8 mm) in diameter. The glans penis is frequently involved. An oral examination may reveal the classic serpiginous white streaks on the buccal mucosa (see Fig. 12-15). Figure 18-10 shows lichen planus of the penis (see also Fig. 8-99).
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