An 18-year-old boy presents with digital gangrene in third and fourth fingers for last 2 weeks. On examination the blood pressure is 170/110 mm of Hg and all peripheral pulses were palpable. food and urine examinations were unremarkable.Antinuclear antibodies, antibody to double stranded NA and antineutrophil cytoplasmic antibody were negative. The most likely diagnosis is :