A 62-year-old man comes to the office due to an intensely pruritic facial rash for the past 3 days. The patient uses no facial cosmetic products but has frequently dyed his hair during the past year; he last dyed his hair 5 days ago and also recalls developing a similar rash the previous time he used hair dye. The patient has a history of asthma, hypertension, and diabetes mellitus. He does not use tobacco, alcohol, or illicit drugs. Vital signs are within normal limits. Physical examination findings are shown in the exhibit.

Which of the following are primarily involved in the pathogenesis of this patient's rash?

Question

A 62-year-old man comes to the office due to an intensely pruritic facial rash for the past 3 days.  The patient uses no facial cosmetic products but has frequently dyed his hair during the past year; he last dyed his hair 5 days ago and also recalls developing a similar rash the previous time he used hair dye.  The patient has a history of asthma, hypertension, and diabetes mellitus.  He does not use tobacco, alcohol, or illicit drugs.  Vital signs are within normal limits.  Physical examination findings are shown in the exhibit. 
 
Which of the following are primarily involved in the pathogenesis of this patient's rash?

Quizplus · Accepted Answer

11ec160b_37c7_4488_9249_2b9eb605da60_MD0001_00 This patient developed erythema and pruritus on the scalp, face, and neck 2 days after reexposure to hair dye. Hair products, including dye, frequently contain allergenic molecules (eg, p-phenylenediamine) that can cause allergic contact dermatitis (ACD). ACD is a type IV (delayed-type) hypersensitivity reaction that occurs in 2 phases: Sensitization: Cutaneous Langerhans cells take up haptens (small molecules that bind to proteins and alter their immune appearance) and present hapten-peptide complexes to naive CD4⁺ and CD8⁺ T cells in regional lymph nodes, resulting in clonal expansion of hapten-sensitive T cells. This phase takes 10-14 days and does not result in cutaneous lesions. Elicitation: On reexposure to the hapten, sensitized T cells are recruited to skin for activation by hapten-protein conjugates displayed on cutaneous antigen-presenting cells. Activated CD8⁺ T cells, the main effector cells in ACD, release cytotoxins (eg, perforin, granzymes) and express Fas ligand to induce keratinocyte apoptosis. They also amplify the inflammatory response by releasing cytokines (eg, interferon gamma) and recruiting additional inflammatory cells (eg, macrophages). This phase occurs 2-3 days following reexposure to the hapten and results in erythema, pruritus, and vesicles. (Choice B) Mast cells are primarily responsible for immediate (type I) hypersensitivity reactions. On reexposure, allergens bind to allergen-specific IgEs on mast cells, causing immediate degranulation and release of vasoactive peptides (eg, histamine), resulting in urticaria and, when severe, anaphylaxis. Onset is rapid (minutes), unlike this patient's delayed (48-hr) response. Furthermore, individual wheals of urticaria resolve within 24 hours, rather than days. (Choice C) Neutrophils phagocytose bacteria and fungi and kill them by generating reactive oxygen species (NADPH oxidase) and hypochlorous acid (myeloperoxidase). Although neutrophils play a role in defense against cutaneous infections (eg, cellulitis, which is painful rather than pruritic), this patient's rash is more consistent with contact dermatitis. (Choice D) Immunoglobulins produced by plasma cells are responsible for type II and III hypersensitivity reactions. ACD does not involve plasma cells or antibodies. (Choice E) Regulatory T cells are CD4⁺ lymphocytes that play an inhibitory role in the immune response. They secrete cytokines (eg, interleukin-10) that inhibit macrophage function and antagonize proinflammatory cytokines (eg, interferon gamma). This anti-inflammatory effect is important in suppressing autoimmune diseases. Educational objective: Allergic contact dermatitis is a type IV (delayed-type) hypersensitivity reaction. Initially, Langerhans cells present haptens to naive T cells, leading to clonal expansion. On reexposure, sensitized CD8⁺ T cells are recruited to skin and destroy tissue. Release of interferon gamma by T cells further amplifies the immune response. __________ References: Type IV hypersensitivity reaction. (http://www.ncbi.nlm.nih.gov/pubmed/32965899)

A 62-Year-Old Man Comes to the Office Due to an Intensely