Dermatology MCQ 5 Questions For USMLE PLAB DHA MOH

Dermatology MCQ 5 Questions For USMLE PLAB DHA MOH

Which of the following determines the primary mechanical properties of skin?

A. Dermis

B. Stratum basale

C. Stratum granulosum

D. Stratum Lucidum

E. Stratum corneum ✅

Question Explanation:

The stratum corneum is the last layer and provides a mechanical barrier to the skin, therefore, determines the mechanical functions of the skin. The hands and feet have thick stratum corneum as compared to the lips and eyelids. The thicker the stratum corneum, the more protection is for the skin. The dermis also has some factor to play with its elastic fibers and fibrous tissue. The rest of the layers are also important but the mechanical properties are primarily determined by the stratum corneum.

A 23-year-old female presents with a history of increasing fatigue, malaise, muscle pains and arthralgia of the wrists and ankles. Recently she had also noted a symmetrical rash on her cheeks and some hair loss. What is the most likely diagnosis?

A. Dermatomyositis

B. Hypothyroidism

C. Porphyria cutanea tarda

D. Rheumatic fever

E. Systemic lupus erythematosus (SLE) ✅

Question Explanation:

This woman has clinical features consistent with systemic lupus erythematosus. She gives a history of fatigue which occurs in almost all SLE patients. Arthralgia and arthritis are the most common presenting manifestations of SLE typically affecting the small joints of the hands, wrists and knees. The symmetrical rash is the classical butterfly rash that occurs in a malar distribution. Alopecia is common and may be diffuse or patchy. In dermatomyositis there is proximal, symmetrical muscle weakness that progresses over weeks to months. The typical lilac papular rash occurs over the dorsum of the metacarpophalangeal (Gottron's papules), elbows and knees.

Hypothyroidism does not result in a symmetrical facial rash. Rheumatic fever characteristically lacks a facial rash and it consists of nodules and there is no history of pharyngitis present. Raynaud's phenomenon is an early symptom. Skin changes include telengiectasia, hyper- and hypo-pigmentation. Sarcoidosis can present acutely with arthritis and erythema nodosum.

A 34-year-old female is admitted with classical "target lesion" appearance, with a pink-red ring around a pale center and erythematous lesions of the mouth and eyes. Which one of the following drugs may account for her presentation?

A. Diazepam

B. Fluoxetine

C. Mebeverine

D. Oestrogen

E. Phenytoin ✅

Question Explanation:

This is characteristic of erythema multiforme. Any drug or infection can trigger EM but drug reactions, most commonly to sulfa drugs, phenytoin, barbiturates, penicillin, and allopurinol, or a host of internal ailments are also responsible.

Which of the following statements regarding psoriasis is correct?

A. 1% of patients have associated psoriatic arthropathy

B. Guttate psoriasis consists of widespread inflammation and exfoliation of the skin

C. Psoriasis is more common at lower geographical altitudes

D. The most common form is plaque psoriasis ✅

E. The prevalence in the United Kingdom is 10%

Question Explanation:

The commonest form of psoriasis is plaque psoriasis, making up approximately 80% of cases (guttate -10%, erythrodermic - 3%, pustular -3%).

Psoriatic erythroderma (erythrodermic psoriasis) involves the widespread inflammation and exfoliation of the skin over most of the body surface

The prevalence of psoriasis is reported as between 0.5 and 4.6%. For reasons which may be explained by the filtering of ultraviolet B (UVB) light, psoriasis is more common at higher altitudes. Studies report:

A high prevalence of psoriatic arthropathy in patients with cutaneous psoriasis and

Arthropathy precedes cutaneous lesions in 20%

• Cutaneous lesions precede joint disease in 60-70% and

• They occur simultaneously in 10-20%.

A 56-year-old woman presents with two months old several, circular, erythematous, raised, smooth-surfaced lesions. Size ranges from 1-5 cms in diameter on the elbows, extensor aspects of the forearms and knuckles. What is the most likely diagnosis?

A. Eczema

B. Psoriasis

C. Granuloma annulare ✅

D. Tinea corporis

E. Lichen Planus

Question Explanation:

The history of non-itchy, circular, raised, smooth-surfaced lesions the elbows, extensor aspects of the forearms and knuckles and the raised borders are suggestive of granuloma annulare.

Discoid eczema tends to be scaly and pruritic in nature.

Psoriasis typically has a silvery scale and can be pruritic.

The typical rash of lichen planus is well-described by the "5 Ps": well-defined pruritic, planar, purple, polygonal papules.

Tinea corporis is a fungal infection and is typically scaly and pruritic in nature.

The most likely answer is therefore granuloma annulare. This can be associated with diabetes.

                      NEXT