Dermatological Conditions of the Foot Flashcards

A patient presents with a well-demarcated, erythematous plaque with silvery scales on the heel. Nail pitting is also noted. What is the most likely diagnosis?

Answer: Psoriasis

Psoriasis on the foot typically presents as well-demarcated erythematous plaques with silvery scales, and nail pitting is a classic associated finding.

Which layer of the epidermis is primarily affected in hyperkeratosis of the foot?

Answer: Stratum corneum

Hyperkeratosis involves thickening of the stratum corneum, the outermost layer of the epidermis.

A diabetic patient develops a painless, punched-out ulcer over the first metatarsal head. What is the primary pathophysiological mechanism?

Answer: Peripheral neuropathy

Neuropathic ulcers in diabetics occur over pressure points due to loss of protective sensation from peripheral neuropathy.

Pityriasis rubra pilaris affecting the foot characteristically produces which finding?

Answer: Islands of sparing within diffuse erythema

Pityriasis rubra pilaris classically shows islands of normal skin (sparing) within an otherwise diffuse erythroderma.

A child presents with painless, flesh-colored papules on the sole with a central dell. What is the treatment of choice?

Answer: Cantharidin application

Molluscum contagiosum on the foot is treated with cantharidin, which induces blistering and destruction of the lesion.

Which dermatophyte species most commonly causes tinea unguium (onychomycosis) of the toenails?

Answer: Trichophyton rubrum

Trichophyton rubrum is responsible for the majority of toenail onychomycosis cases worldwide.

A patient with chronic venous insufficiency develops a brown discoloration around the medial malleolus. This pigmentation is caused by:

Answer: Hemosiderin deposits from RBC extravasation

Hemosiderin staining occurs when red blood cells extravasate into the dermis due to venous hypertension and break down, releasing iron pigment.