Okay, let's tackle this question. The patient has melaena, which suggests upper GI bleeding. Normal renal function and hypertension are there. Also, mononeuritis multiplex is mentioned. Mononeuritis multiplex is when multiple nerves are affected, often due to vasculitis or diabetes. But since renal function is normal, diabetes might be less likely here. Hypertension could be a clue. Mononeuritis multiplex can be part of vasculitis, like in granulomatosis with polyangiitis (GPA), but GPA also affects the upper respiratory tract. Another possibility is systemic vasculitis such as polyarteritis nodosa (PAN). PAN is associated with hypertension, renal involvement, but in this case, renal function is normal. Wait, PAN can affect the kidneys, but if it's not present here, maybe another condition. Oh, Churg-Strauss syndrome? No, that's with asthma and eosinophilia. Hmm. Another possibility is Behçet's disease, but that's more with oral ulcers and uveitis. Wait, the patient has mononeuritis multiplex and hypertension. Maybe it's a vasculitis that affects small vessels. Let's think again. PAN is a medium vessel vasculitis, but it can cause mononeuritis multiplex. However, PAN often involves the kidneys, but the question states normal renal function. So maybe another vasculitis. Wait, maybe it's Henoch-Schönlein purpura? No, that's more in children and has palpable purpura. Alternatively, the patient could have a condition that causes vasculitis without renal involvement. Oh, wait! The combination of melaena (upper GI bleed), hypertension, mononeuritis multiplex, and normal kidney function might point to a specific diagnosis. Let me think about the differential. If the patient has vasculitis involving the gastrointestinal tract and peripheral nerves, but not the kidneys, maybe it's polyarteritis nodosa? But PAN usually affects the kidneys. Wait, maybe the patient has a different vasculitis. Another angle: melaena could be from a vasculitic GI lesion. Mononeuritis multiplex is often seen in vasculitis. Hypertension is a common feature in PAN, which is a medium vessel vasculitis. PAN can involve the GI tract, leading to bleeding, and peripheral nerves. But if renal function is normal, maybe the disease is in an early stage or not affecting the kidneys. So the most probable diagnosis here would be polyarteritis nodosa. Let me confirm. PAN is associated with hypertension (due to renal artery involvement), GI involvement (which can cause bleeding), and peripheral neuropathy (mononeuritis multiplex). Since renal function is normal, perhaps the renal arteries aren't involved yet, or the damage isn't severe enough to affect function. So the answer is polyarteritis nodosa.

**Core Concept**
The question tests recognition of systemic vasculitis with gastrointestinal and neurological manifestations. Key features include melaena (GI bleeding), mononeuritis multiplex (vasculitic neuropathy), and hypertension (common in polyarteritis nodosa).

**Why the Correct Answer is Right**
Polyarteritis nodosa (PAN) is a medium-vessel vasculitis causing ischemia in multiple organs. It classically presents with

✓ Correct Answer: A. Classical polyarteritis nodosa