**Question:** A 30 years old male patient presents with complaints of weakness in right upper and both lower limbs of last 4 months. He developed digital infarcts involving 2nd and 3rd fingers on right side and 5th finger on left side. On examination, BP was 160/140 mm Hg, all peripheral pulses were palpable and there was asymmetrical neuropathy. Investigations showed a Hb of 12 gm, TLC - 12000 Cu mm, Platelets - 4,30,000, ESR - 49 mm. Urine examination showed proteinuria and RBC -10-15/ hpf with no casts. Which of the following is the most likely diagnosis?

A. Polyarteritis nodosa
B. Systemic lupus erythematosus
C. Systemic sclerosis
D. Granulomatosis with polyangiitis (Wegener's granulomatosis)

**Correct Answer:** A. Polyarteritis nodosa

**Core Concept:**

Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis affecting small and medium-sized arteries, typically seen in middle-aged adults. It causes inflammation and damage to the arterial walls leading to ischemia and necrosis of the affected tissues. In this case, the clinical presentation of weakness in upper and lower limbs and digital infarcts in the fingers are consistent with PAN's characteristic manifestations.

**Why the Correct Answer is Right:**

A) Polyarteritis nodosa is the most likely diagnosis in this case because of the following reasons:

1. Clinical presentation: The patient presents with bilateral lower limb weakness, which is a common presentation of PAN affecting the lower limbs.
2. Digital infarcts: PAN can cause digital infarcts due to its effect on the arteries supplying the extremities, leading to ischemia and necrosis of the affected tissues.
3. Uveitis: PAN can also present with uveitis, which is seen in up to 50% of cases.
4. Rheumatoid factor: About 70% of PAN patients show positive rheumatoid factor, which is not specific to PAN but is more common in this condition than other vasculitides.

**Why Other Options Are Incorrect:**

B) Systemic lupus erythematosus (SLE): Although SLE can cause digital infarcts (due to arterial occlusion), it is less common than PAN and is typically associated with other autoimmune manifestations like arthritis, photosensitivity, and oral ulcers.

C) Systemic sclerosis (scleroderma): This condition primarily affects small vessels (capillaries) and skin, leading to scleroderma and Raynaud's phenomenon, respectively. Digital infarcts are less common in scleroderma compared to PAN.

D) Granulomatosis with polyangiitis (GPA): While GPA can cause digital infarcts, it is less common than PAN and is more likely to present with pulmonary and renal involvement than PAN.

**Clin