Okay, let's tackle this question. The patient is an 18-year-old boy with digital gangrene on the third and fourth fingers. His BP is really high at 170/110, which is hypertensive. All peripheral pulses are palpable, so it's not an arterial occlusion. Blood and urine tests are normal, and the ANA, anti-dsDNA, and ANCA are negative. So, what's going on here?

Digital gangrene can be due to various causes like trauma, embolism, vasculitis, or thromboangiitis obliterans (Buerger's disease). But Buerger's is more common in smokers and usually affects the hands and feet. However, the patient is 18, so maybe a smoker? But the question doesn't mention that. Also, Buerger's is associated with peripheral vascular occlusion, but here pulses are palpable.

High blood pressure is a red flag. Hypertension can lead to accelerated atherosclerosis, but that's more common in older people. Maybe it's a case of hypertensive emergency causing digital ischemia? But usually, that's more generalized. Another possibility is thromboangiitis obliterans, but again, ANCA is negative.

Wait, the ANCA is negative, so Wegener's granulomatosis is out. The ANA and anti-dsDNA are negative, so lupus or SLE isn't the cause. What about other vasculitides? Maybe Henoch-Schönlein purpura, but that's more in children and has a rash.

Hypertensive retinopathy is a thing, but the question mentions digital gangrene. Maybe it's a case of malignant hypertension leading to microvascular damage. Malignant hypertension can cause retinal changes and end-organ damage like digital gangrene. The high BP here (170/110) is stage 2, but malignant hypertension is a hypertensive emergency with end-organ damage. Since the patient has digital gangrene, that's end-organ damage. The negative autoimmune markers rule out vasculitis. So the most likely diagnosis here is malignant hypertension leading to digital gangrene.

The options might include other vasculitides or Buerger's, but given the negatives and the hypertension, malignant hypertension is the answer.

**Core Concept**
Digital gangrene in a young patient with severe hypertension but negative autoimmune markers suggests **malignant hypertension** as a cause of microvascular occlusion. This condition leads to end-organ damage via accelerated atherosclerosis and fibrinoid necrosis of small vessels.

**Why the Correct Answer is Right**
Malignant hypertension (diastolic >120 mmHg) causes **malignant nephrosclerosis** and **retinopathy**, but can also induce digital gangrene via microvascular thrombosis. The absence of ANA, anti-dsDNA, and ANCA rules out lupus, vasculitis, and Wegener’s granulomatosis. Palpable pulses suggest no major arterial occlusion, supporting microvascular pathology over macrovascular disease.

**Why Each Wrong Option is Incorrect**
**Option A:** *Thromboangiitis obliterans (Buerger’s disease)* requires tobacco use and affects young males, but it causes segmental

✓ Correct Answer: B. Polyarteritis nodosa