USMLE Step 2 Sample Questions

The correct answer is D. Cell-mediated/delayed (type IV)

Explanations: Cell-mediated/delayed (type IV). TRUE: Allergic-contact dermatitis is a T-cell-mediated, delayed-type hypersensitivity response to external agents, resulting in a geometric lesion corresponding to the region of contact. Contact allergens include metals (classically nickel), glues, rubber, plastics, fragrances, preservatives, topical antibiotics, and chemicals found in hair care and cosmetic products. The hands, face, or eyelids, which commonly come in contact with the environment, are most often involved. The dominant symptom is itching. However, burning, stinging, or pain may also be symptoms of contact dermatitis. Allergic-contact dermatitis presents as a well-demarcated, pruritic, eczematous eruption localized to the area of skin that comes in contact with the allergen. However, the allergen itself or the secondary transfer of the allergen from the primary contact site may cause patchy or diffuse distributions. Diagnosis relies on the clinical features, history of allergen exposure, lab tests, patch testing, and/or lack of recurrence after removal of suspected allergen. Patients with allergic-contact dermatitis often have a history of atopy, such as asthma, hay fever, or conjunctivitis.

Anaphylactic (type I). FALSE: Type I reactions (immediate hypersensitivity reactions) involve the IgE-mediated release of histamine and other mediators from mast cells and basophils.

Cytotoxic (type II). FALSE: Type II reactions (cytotoxic hypersensitivity reactions) involve immunoglobulin G or immunoglobulin M antibodies bound to cell surface antigens, with subsequent complement fixation.

Immune complex-mediated (type III). FALSE: Type III reactions (immune-complex mediated reactions) involve circulating antigen-antibody immune complexes that deposit in postcapillary venules, with subsequent complement fixation

Autoimmune disease (type V). FALSE: In the traditional classification of hypersensitivity reactions developed by Gell and Coombs, a type V classification is not used. Type V hypersensitivity is used in the UK to refer to receptor-mediated autoimmune disease such as Graves’ disease or myasthenia gravis, which would fall under type II in the traditional classification.