DPM Dermatological Conditions of the Foot 2 — Questions and Answers
Question 1: 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?
- Tinea pedis
- Psoriasis (Correct answer)
- Contact dermatitis
- Pityriasis rosea
Correct answer: Psoriasis
Psoriasis on the foot typically presents as well-demarcated erythematous plaques with silvery scales, and nail pitting is a classic associated finding.
Question 2: Which layer of the epidermis is primarily affected in hyperkeratosis of the foot?
- Stratum basale
- Stratum spinosum
- Stratum corneum (Correct answer)
- Stratum granulosum
Correct answer: Stratum corneum
Hyperkeratosis involves thickening of the stratum corneum, the outermost layer of the epidermis.
Question 3: A diabetic patient develops a painless, punched-out ulcer over the first metatarsal head. What is the primary pathophysiological mechanism?
- Venous insufficiency
- Peripheral neuropathy (Correct answer)
- Arterial occlusion
- Autoimmune vasculitis
Correct answer: Peripheral neuropathy
Neuropathic ulcers in diabetics occur over pressure points due to loss of protective sensation from peripheral neuropathy.
Question 4: Pityriasis rubra pilaris affecting the foot characteristically produces which finding?
- Vesicular eruption
- Islands of sparing within diffuse erythema (Correct answer)
- Pustules on the arch
- Linear streaks of hyperpigmentation
Correct answer: Islands of sparing within diffuse erythema
Pityriasis rubra pilaris classically shows islands of normal skin (sparing) within an otherwise diffuse erythroderma.
Question 5: A child presents with painless, flesh-colored papules on the sole with a central dell. What is the treatment of choice?
- Topical antifungal
- Cantharidin application (Correct answer)
- Oral acyclovir
- Intralesional corticosteroid
Correct answer: Cantharidin application
Molluscum contagiosum on the foot is treated with cantharidin, which induces blistering and destruction of the lesion.
Question 6: Which dermatophyte species most commonly causes tinea unguium (onychomycosis) of the toenails?
- Microsporum canis
- Trichophyton rubrum (Correct answer)
- Epidermophyton floccosum
- Trichophyton tonsurans
Correct answer: Trichophyton rubrum
Trichophyton rubrum is responsible for the majority of toenail onychomycosis cases worldwide.
Question 7: A patient with chronic venous insufficiency develops a brown discoloration around the medial malleolus. This pigmentation is caused by:
- Melanin deposition
- Hemosiderin deposits from RBC extravasation (Correct answer)
- Bile pigment accumulation
- Carotenoid deposits from diet
Correct 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.
DPM Dermatological Conditions of the Foot 2
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?