Subcutaneous bleeding is caused by collagen abnormalities in the vessel wall. The high frequency of a bleeding tendency in Ehlers-Danlos patients with normal tests for haemostasis (83%) supports the conventional explanation for this clinical feature. It shows that the defects in the structural integrity of skin and blood vessels lead to easy bruising.
Resources: [Anstey A, Mayne K, Winter M, Van de Pette J, Pope FM. "Platelet and coagulation studies in Ehlers-Danlos syndrome." Br J Dermatol. 1991 Aug;125(2):15563). Disorders of Vascular Fragility, Reed E. Pyeritz MD, PhD Vol 29; (6): 2001.]
Pepin M, Schwarze U, Superti-Furga A, Byers PH. “Clinical and genetic features of Ehlers-Danlos syndrome type IV, the Vascular Type.” N Engl J Med. 2000 Mar; 342(10):673–80. Erratum in: N Engl J Med 2001 Feb 1;344(5):392.