John F. Rupp, MD

Dermatophyte infections have a predilection for certain anatomic sites, such as the feet, groin, and scalp. Tinea corporis refers to involvement of the trunk and extremities. The condition arises either from direct exposure to an infected source or by extension from an adjacent affected site. Itch is a common symptom, but the intensity of the pruritus can vary from patient to patient.

The onset of atopic dermatitis can be seen in infants who have a family history of inhalant allergies, (eg, seasonal allergy, allergic rhinitis, or allergy-induced asthma). The cheeks and large flexural folds of affected children are erythematous and scaly. Involved areas of the trunk and extremities may exhibit discrete patches or a generalized rash.

Lichen planus is characterized by flat-topped, polygonal, purple pruritic papules that have a predilection for flexor aspects of the wrists and forearms, sides of the neck, thighs, shins, and lower back. Lesions on the oral mucosa appear as white, lacy patches.

Persistent, unremitting itch-which intensifies at night-is the chief complaint of patients with scabies. The female Sarcoptes scabiei mite (A) burrows into the stratum corneum, where she lays eggs. The parasite is transferred by intimate contact and fomites, such as infested clothing, towels, and bedding.

This self-limited eruption is characterized by erythematous, scaling, oval-shaped macules on the trunk and proximal extremities. Most outbreaks begin with a single, large patch-a mother or herald patch-that typically is found on the trunk. Commonly, this lesion is confused with ringworm.