View source for WBR0769

 {{WBRQuestion
|QuestionAuthor= {{SSK}}(Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|SubCategory=Dermatology
|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Dermatology
|Prompt=A 14 year-old-boy is brought to the physician's office by his mother for multiple pruritic lesions on his legs. The mother informs the physician that the child had recently returned from a picnic and she fears he has been exposed to poison ivy. On physical examination, the physician notes vesicular bullous lesions with erythema on the lower extremities. The patient's condition is best characterized by a hypersensitivity disorder that resembles which other disease?
|Explanation=The patient in this scenario is presenting with contact dermatitis following exposure to poison ivy, a common irritant. Poison ivy triggers Toxicodendron dermatitis (named after plant genus) due to the presence of urushiol, a clear liquid compound produced by the plant. Patients have varied reactions to poison ivy, with 25% of patients having no reaction, and 25% having a very severe eruption. The rash usually appears within 24 hours and resolves within 2 weeks. It may sometimes require topical steroids. Contact dermatitis is a type IV or delayed hypersensitivity reaction. The disease mechanism closely resembles that of Crohn's disease that is also considered a type IV hypersensitivity disorder. In a type IV reaction, CD8+ cytotoxic T cells recognize the antigen in a complex with class II MHC complex on antigen presenting cells. Activated CD8+ T cells then destroy target cells on contact. In Crohn's disease, delayed hypersensitivity reactions are suggested by the characteristic inflammatory granulomas along the GI tract. Treatment in patients with severe disease consists of TNF-alpha antagonists to attenuate the autoimmune reaction. Other diseases that are also classified as type IV hypersensitivity disorders include: multiple sclerosis, Guillain-Barre syndrome, graft-vs-host disease, and PPD testing for ''Mycobacterium tuberculosis''.
|AnswerA=Pernicious anemia
|AnswerAExp=Pernicious anemia is a type II hypersensitivity disorder.
|AnswerB=Crohn's Disease
|AnswerBExp=Crohn's disease is an example of a type IV hypersensitivity disorder.
|AnswerC=Systemic lupus erythematosus (SLE)
|AnswerCExp=Certain manifestations of SLE are caused by a type III hypersensitivity reaction.
|AnswerD=Atopic dermatitis
|AnswerDExp=Eczema or atopic dermatitis is caused by a type I hypersensitivity disorder.
|AnswerE=Poststreptococcal  glomerulonephritis (PSGN)
|AnswerEExp=PSGN is a caused by a type III hypersensitivity disorder.
|EducationalObjectives=Contact dermatitis and Crohn's disease are both caused by type IV hypersensitivity reactions.
|References=First Aid 2014 page 208-209
|RightAnswer=B
|WBRKeyword=Crohn's disease, Guillain-Barre, Multiple sclerosis, Type IV hypersensitivity, Type III hypersensitivity, Hypersensitivity disorder, Hypersensitivity, Dermatitis, Irritant, Allergic, Allergy, Atopic, Atopy
|Approved=Yes
}}