**Core Concept**
The patient's presentation of abdominal pain, rashes, palpable purpura, and arthritis suggests a systemic vasculitis, specifically affecting small vessels. This condition is characterized by inflammation of the blood vessels, leading to damage and disruption of blood flow, which in turn causes the observed symptoms.

**Why the Correct Answer is Right**
The patient's symptoms are most consistent with Henoch-Schönlein purpura (HSP), a form of small vessel vasculitis. HSP is characterized by the deposition of IgA immune complexes in the walls of small blood vessels, leading to inflammation and damage. The classic tetrad of symptoms in HSP includes palpable purpura, abdominal pain, arthritis, and renal involvement. The presence of IgA deposits in the affected tissues is a hallmark of this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect as it does not match the patient's presentation of palpable purpura and abdominal pain. While it may present with similar symptoms, it is not the most probable diagnosis.

**Option B:** This option is incorrect as it does not account for the patient's systemic symptoms, including abdominal pain and arthritis. It is a more localized condition.

**Option C:** This option is incorrect as it does not match the patient's presentation of palpable purpura and abdominal pain. It is a more severe form of vasculitis that typically affects larger vessels.

**Clinical Pearl / High-Yield Fact**
Henoch-Schönlein purpura is a classic example of a small vessel vasculitis, and the deposition of IgA immune complexes is a key pathophysiological mechanism. This condition often affects children and young adults, and renal involvement is a significant concern.

**Correct Answer: D. Henoch-Schönlein purpura**