Petechiae in scurvy is due to
Vitamin C deficiency causes defective formation of collagen with impaired healing of wounds, capillary haemorrhage and reduced platelet adhesiveness (normal platelets are rich in ascorbate) . Petechiae are formed due to minor bleeds from capillary vessels due to endothelial disintegration . Ref - Davidson 23e p716
Platelet dysfunction
Thrombocytopenia
Clotting factor deficiency
Endothelial disintegration
Nutrition