Which of the following is false about polyarteritis nodosa
**Core Concept**
Polyarteritis nodosa (PAN) is a systemic vasculitis that affects medium and small-sized arteries, leading to necrotizing inflammation and aneurysmal formation. It is characterized by the presence of a necrotizing inflammatory process in the arterial wall, without granuloma formation.
**Why the Correct Answer is Right**
PAN is a non-granulomatous vasculitis, meaning it does not involve the formation of granulomas, which are aggregates of immune cells that attempt to wall off foreign substances. This distinguishes PAN from other forms of vasculitis, such as granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis). The lack of granulomas in PAN is due to the absence of a significant immune response to an antigen, and instead, the inflammation is thought to be driven by immune complex deposition and complement activation.
**Why Each Wrong Option is Incorrect**
* **Option A:** PAN typically affects medium-sized arteries, but it can also involve small arteries and arterioles. This option may be incorrect, but without more information, it's hard to say for sure.
* **Option B:** PAN is characterized by the presence of aneurysms, which are outpouchings of the arterial wall. This option is likely incorrect because aneurysms are a hallmark of PAN.
* **Option C:** PAN is a type of necrotizing vasculitis, meaning that it involves the destruction of the arterial wall. This option is likely incorrect because necrotizing vasculitis is a defining feature of PAN.
**Clinical Pearl / High-Yield Fact**
PAN can present with a wide range of symptoms, including hypertension, renal failure, and gastrointestinal bleeding. It's essential to consider PAN in the differential diagnosis of patients with systemic symptoms and vasculitis.
**Correct Answer: B. PAN is characterized by the presence of aneurysms, which are outpouchings of the arterial wall.**