This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Skin
[{'content': 'A 30 years old male presented with silvery scales on elbow and knee, which bleed on removal. The probable diagnosis is: \nSelect and explain. \nA. Pityriasis, B. Seborrheic dermatitis, C. Psoriasis, D. Secondary syphilis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C. PsoriasisPsoriasis* Silvery white scales (due to air trapped between scales)* Removal of scales lead to appearance of punctuation/ pinpoint bleeding points (Auspitz sign)* Grattage test: Scratching with a glass slide accentuates scale formation in a psoriatic plaque.* Scales are absent in flexural psoriasis and on glans in un-circumscribed patients* Scaling is profuse in elephantine and rapid psoriasis.Seborrheic dermatitis* Greasy scalesPityriasis rosea* Collarette scales which are attached to peripheral edge and free towards center', 'role': 'assistant'}]