Diffuse mesangial and paramesangial dense deposits on electron microscopy are seen in
**Core Concept**
The question is testing the student's knowledge of **glomerulonephritis** and the characteristic findings on **electron microscopy**. Specifically, it's about identifying the pattern of immune complex deposition in different types of glomerulonephritis.
**Why the Correct Answer is Right**
The correct answer is related to the **mesangial** and **paramesangial** regions of the glomerulus, where immune complexes can deposit. In **IgA nephropathy**, also known as **Berger's disease**, electron microscopy typically shows **diffuse mesangial and paramesangial dense deposits**. This pattern is characteristic of IgA nephropathy, which is the most common cause of glomerulonephritis worldwide.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not typically show the described pattern of immune complex deposition.
**Option B:** This option is incorrect because it is associated with a different pattern of injury.
**Option C:** This option is incorrect because it is associated with **subepithelial deposits**.
**Option D:** This option is incorrect because it is associated with **pauci-immune** type of injury.
**Clinical Pearl / High-Yield Fact**
IgA nephropathy is a common cause of recurrent **hematuria** and can progress to **end-stage renal disease**. The diagnosis is often made by **renal biopsy**.
**Correct Answer:** D. IgA nephropathy.