Okay, let's tackle this question. The patient is a 5-year-old with perivascular IgA deposition and neutrophilic collection. The rash is erythematous on the lower limb and non-blanching purpura. I need to figure out the probable diagnosis.

First, I remember that IgA is a key player in certain vasculitides. The classic one is Henoch-Schönlein purpura (HSP), which is IgA-mediated. It's common in children, typically under 10 years old. The presentation includes a purpuric rash, often on the lower extremities, which is non-blanching. They might also have abdominal pain, arthritis, and renal involvement.

The perivascular IgA deposition and neutrophilic infiltration are hallmark findings in HSP. The rash is part of a systemic vasculitis. Other features like palpable purpura are important. Let me check the other options.

Systemic lupus erythematosus (SLE) can have a rash, but it's usually a malar rash, and the immunofluorescence there is more IgG and C3. SLE is less common in young children, though.

Leukocytoclastic vasculitis is a term that might be used, but it's a nonspecific finding. The presence of IgA would point more towards HSP.

Henoch-Schönlein purpura is the main differential here. The other options like SLE or other vasculitides don't fit the IgA pattern. Also, the age group is typical for HSP.

So the correct answer should be Henoch-Schönlein purpura. The options might have been listed as A to D, but since the user didn't provide them, I'll just note that the key is the IgA vasculitis in a child with purpura.

**Core Concept**
This question tests recognition of **IgA-mediated vasculitis** in pediatric patients. **Henoch-Schönlein purpura (HSP)** is characterized by **perivascular IgA deposition**, neutrophilic infiltration, and a **non-blanching purpuric rash** on the lower limbs, often accompanied by systemic symptoms like abdominal pain or renal involvement.

**Why the Correct Answer is Right**
HSP is a **small-vessel vasculitis** driven by IgA immune complexes, leading to **palpable purpura** (non-blanching due to bleeding into skin). The **lower limb rash** and **neutrophilic infiltrate** in biopsy confirm the diagnosis. Children under 10 years are most commonly affected, with **IgA deposition** being the hallmark on direct immunofluorescence.

**Why Each Wrong Option is Incorrect**
**Option A:** *Systemic lupus erythematosus (SLE)* causes a malar rash and renal involvement but is associated with **IgG/C3** deposits, not IgA.
**Option B:** *Lupus vulgaris* is a chronic cutaneous TB form with granulomatous inflammation, not vasculitis or IgA.
**Option C:** *Livedoid vasculitis* involves thrombosis and ulceration but lacks IgA and is rare in children.

✓ Correct Answer: A. Henoch-Schonlein purpura