Merck Manual

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Overview of Bleeding Caused by Abnormal Blood Vessels

By

David J. Kuter

, MD, DPhil, Harvard Medical School

Full review/revision Oct 2021 | Modified Sep 2022
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Bleeding may result from abnormalities in

Collagen is a protein that is important in maintaining strong blood vessels in the body. When collagen is abnormal or abnormal substances in the blood get into vessel walls, the vessels weaken and bleeding can develop.

Fragile blood vessels cause bleeding under the skin, leading to tiny red, purple or brown spots on the skin (petechiae), red or purple blemishes or bruises (purpura), and bruising. Most disorders caused by fragile blood vessels do not cause serious blood loss. The genetic disorder hereditary hemorrhagic telangiectasia Hereditary Hemorrhagic Telangiectasia (HHT) Hereditary hemorrhagic telangiectasia is a hereditary disorder in which blood vessels are malformed, making them fragile and prone to bleeding. Dilated blood vessels (telangiectasia) are present... read more Hereditary Hemorrhagic Telangiectasia (HHT) is an exception.

Blood vessels can also be weakened by deposits of abnormal proteins in their walls Protein Disorders Causing Bruising or Bleeding Conditions that cause an abnormal protein or an abnormal amount of certain normal proteins in the blood can cause blood vessels to become fragile. When these fragile blood vessels break, people... read more Protein Disorders Causing Bruising or Bleeding as occurs in amyloidosis Amyloidosis Amyloidosis is a rare disease in which abnormally folded proteins form amyloid fibrils that accumulate in various tissues and organs, sometimes leading to organ dysfunction, organ failure, and... read more Amyloidosis , cryoglobulinemia Cryoglobulinemia Conditions that cause an abnormal protein or an abnormal amount of certain normal proteins in the blood can cause blood vessels to become fragile. When these fragile blood vessels break, people... read more Cryoglobulinemia , and hypergammaglobulinemic purpura Hypergammaglobulinemic purpura Conditions that cause an abnormal protein or an abnormal amount of certain normal proteins in the blood can cause blood vessels to become fragile. When these fragile blood vessels break, people... read more Hypergammaglobulinemic purpura , or by inflammation as in autoimmune vasculitis. For example, bleeding may be a prominent feature of immunoglobulin A–associated vasculitis Immunoglobulin A–Associated Vasculitis Immunoglobulin A–associated vasculitis (formerly called Henoch-Schönlein purpura) is inflammation of mainly small blood vessels that most often occurs in children. A rash of reddish purple bumps... read more Immunoglobulin A–Associated Vasculitis , an inflammation of small blood vessels that is common during childhood.

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