**Question:** A 7-year-old boy presents with palpable non-blanching rash starting 3 days back from the ankles and involves lower limbs and buttocks. He had viral URTI previously. BP is normal and KFT is normal. What is the diagnosis?

A. Erythema infectiosum (fifth disease)
B. Urticaria
C. Dermatomyositis
D. Disseminated intravascular coagulation (DIC)

**Core Concept:**
The question is asking about the correct diagnosis of a 7-year-old boy presenting with a specific rash pattern and clinical history. The rash described is non-blanching and starts from the ankles, involving the lower limbs and buttocks. The patient has a previous history of viral upper respiratory tract infection (URTI). The blood pressure (BP) and kidney function test (KFT) results are within normal limits.

**Why the Correct Answer is Right:**
The correct diagnosis in this case is Erythema infectiosum (fifth disease) also known as slapped cheek syndrome. This is a viral illness caused by the parvovirus B19. The rash pattern described (starting from the ankles and involving lower limbs and buttocks) is a characteristic feature of this disease. The boy has had a previous viral URTI, which is the typical mode of transmission for parvovirus B19. Additionally, the rash does not blanch upon pressing, which is a key feature of Erythema infectiosum.

**Why Other Options are Incorrect:**
B. Urticaria: Urticaria (hives) is characterized by blanching rash due to increased vascular permeability. It usually occurs suddenly and resolves rapidly, whereas Erythema infectiosum presents gradually and lasts for several days.

C. Dermatomyositis: Dermatomyositis is an autoimmune disorder affecting the skin and muscles, usually accompanied by muscle weakness and involvement of other organs. The rash in dermatomyositis is characteristically erythematous and non-blanching, but it does not begin from the ankles and involves the lower limbs and buttocks.

D. Disseminated intravascular coagulation (DIC): DIC is a severe complication of severe sepsis or trauma, characterized by abnormal coagulation and bleeding tendency. It does not present with the described rash pattern and usually has a much more severe clinical presentation, including bleeding diathesis.

**Clinical Pearl:**
Erythema infectiosum (fifth disease) is a common childhood infection caused by parvovirus B19. It is typically seen in children and has a benign clinical course, with mild fever, arthralgia, and the characteristic rash pattern described. It is a viral infection that usually occurs in a primary infection and does not require any intervention.

The correct answer is **Erythema infectiosum (fifth disease)**. It is a viral infection caused by parvovirus B19. The rash pattern, mild fever, arthralgia, and the history of previous viral illness are consistent with the correct