Dermatology MCQ 6 Questions For USMLE PLAB DHA MOH Exams

Dermatology MCQ 6 Questions For USMLE PLAB DHA MOH Exams

A 23-year-old male shows concern about extensive, coalescing, hypopigmented, slightly scaly lesions on his back and chest for two years. It has gradually become more extensive. He has been in good health. The lesions were not symptomatic. What is the most appropriate treatment for his condition?

A. Cytarabine

B. Oral Nystatin

C. Oral itraconazole

D. Ketoconazole cream ✅

E. Oral terbinafine

Question Explanation:

The patient presents with an asymptomatic eruption on his trunk.

The lesions are scaly, hypopigmented and are not associated with any systemic disease.

This is characteristic of pityriasis versicolor, which is caused by the unicellular yeast Pityrosporum ovale and Pityrosporum orbiculare. The yeast is lipophilic and is encouraged by an increase in environmental temperature, thus many patients notice that the condition begins after a summer vacation. It is a disorder of the healthy but the immunocompromised are at risk. The condition is asymptomatic and appears pale in comparison to the normal skin. The fungus affects the melanocytes hence the hypo- pigmentation. The treatment options include topical imidazole creams, selenium sulphide shampoo and if not responding to topical treatment oral itraconazole 200 mg once a day for seven days. In this patient the topical treatment should be tried first.

A 51-year-old male presents with a symmetrical rash over the cheeks, nose chin, with multiple papules and pustules occurring intermittently over the past two years. What is the most appropriate therapy for this patient?

A. Penicillin

B. Ketoconazole

C. Isotretinoin

D. Doxycycline ✅

E. Prednisolone

Question Explanation:

The description is that of acne rosacea particularly in view of the distribution, duration and absence of any other features. The most appropriate treatment is a tetracycline.

Which of the following is true regarding diabetic foot ulceration?

A. Radiography can distinguish between Charcot's joint and osteomyelitis.

B. Autonomic neuropathy results in increased resting blood flow

C. Plantar ulceration is most commonly due to atherosclerosis

D. Callus formation at pressure points does not prove to be a good predictor of ulceration

E. Minor skin trauma is probably the most common initiating event ✅

Question Explanation:

Minor skin trauma is probably the most common initiating event. Callus formation at pressure areas is an important predictor of potential ulceration. Plantar ulceration is usually a consequence of neuropathy. Blood flow is often decreased with autonomic neuropathy hence sympathectomy may be performed to improve skin blood flow. It is difficult to distinguish radiographically between Charcot's joint and osteomyelitis.

Concerning neurofibromatosis Type 1 (NF1), which one of the following statements is true?

A. The diagnosis is likely if two cafe-au-lait patches are present

B. Lisch nodules are in 90% of people ✅

C. Bilateral acoustic neuromas are common

D. Clinical severity in individuals is similar in a given family

E. New mutations occur rarely

Question Explanation:

Lisch nodules of the iris are present in more than 90% of patients. Bilateral acoustic neuromas are a hallmark feature of neurofibromatosis type 2. Expressivity of the gene is highly variable and members of the same family usually show wide differences in clinical symptoms.

NF1 is one of the most common autosomal dominant conditions. However almost half of all cases give no family history and are new mutations. The mutation rate is estimated to be 1:10,000 gametes. The diagnosis is suggested by six or more café-au-lait macules (spots), each over 5 mm in diameter in prepubescent individuals and over 15 mm in postpubertal individuals.

An 8-year-old boy was treated with Permethrin cream for scabies infestation. On follow-up three weeks later, he continues to have the infection. What is the most likely reason?

A. The treatment was not repeated as prescribed

B. Other household members were not treated ✅

C. Facial skin was not treated

D. Non-disposal of clothes

E. The organism is resistant to Permethrin

Question Explanation:

Scabies is an intensely pruritic and highly contagious infestation of the skin, acquired through close personal contact. A delayed type IV hypersensitivity reaction to the mites, their eggs, or excreta occurs approximately 30 days after infestation and is responsible for the intense pruritus that is the hallmark of the disease. All household members and close personal contacts should be treated, whether or not they are symptomatic, and patients should be re-examined 2 weeks after treatment to evaluate effectiveness. Treatment failures are uncommon.

Recurrence of the eruption usually means re-infection has occurred.

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