Bruises are not a pleasant sight, and it’s easy to feel discomfort or concern if your notice a dark or bluish patch in your arms or legs, especially if you don’t recall any trauma in that particular site.
What are bruises and how do they form?
Skin is very vascular. This organ which is the largest in our body with a surface area of more than 2 and a half square meters has to be supplied by a complex network of blood vessels called capillaries. They serve to deliver oxygen and nutrition uniformly to our skin cells. This is the reason why white-skinned individuals especially from Nordic countries have a pinkish tinge to their skin. It can also serve to assess the perfusion of the skin if such tinge is replaced with a pale white color and sometimes, to assess the oxygenation of the blood if such pinkish tinge turns bluish.
Bruises form when blood capillaries are injured, and blood is released into the skin layers. This is not uncommon and the skin -being the interface of our body into the surrounding environment- is very liable to trauma, but the ease of such injury to cause bleeding and the amount of blood released before our hemostatic mechanisms -those which form a blood clot to stop the bleeding- kick in differ according to the individual and the integrity of the hemostatic system.
The bruise has different colors depending on its age and the skin color of the person. People with a lighter skin tone tend to have bruises which are bluish or purplish while those with a darker skin tone have dark purple, brownish or even black bruises. The bruise ages with a change of color due to the change of hemoglobin found in red blood cells released from the ruptured capillaries. On the first 2 days, the bruise is reddish with edema from the release of inflammatory mediators and with the normal color of red cells. Two to five days later, the color becomes bluish with the loss of oxygen that the red cell carries and its attachment to carbon dioxide which causes the hemoglobin to become bluish. A week after the injury, the color becomes greenish due to the conversion of hemoglobin into biliverdin, which is green in color. Biliverdin is then converted to bilirubin -the chemical substance which if released in excess can cause jaundice in some diseases-. Afterwards, the bruise becomes dark brown and slowly begins to disappear.
Are all spots on the skin bruises?
It is a common misconception that any bluish patch or spot on the skin is a “bruise”. While bruises form the majority of spots that appear as bluish, reddish or brownish on the skin of the arms and legs, a common differential diagnosis that is usually considered by physicians is a “rash”. Rash is a general term and can include different shapes and sites of appearance. The rash of herpes, for example, is very different than that of allergy and that of bacterial infections differs from that of scabies. The rash that looks like bruises is called a hemorrhagic rash. It can result from infections including:
- Coxsackievirus A19, which mostly causes mild illnesses
- Echovirus, which can cause a multitude of infections from mild fever-like illnesses to severe infections including meningitis -infection of the coverings of the brain- and endocarditis -infection of the inner lining of the heart and heart valves-.
- Cytomegalovirus, which mostly affects the liver, lymph nodes and the spleen.
- Meningococcemia, which is meningitis caused by Neisseria gonorrhea bacteria. It is a life-threatening infection.
- Bacterial endocarditis can also cause a hemorrhagic rash
Another common differential diagnosis of bruises is what we call a vasculitis rash. Blood vessels can be inflamed in multiple conditions and a rash develops if this inflammation involves the small blood vessels close to the skin. This condition is termed small vessels vasculitis, and the rash resulting from such condition has the special character of being raised above the skin unlike other rashes which are normally on the same level of the skin. Causes of vasculitis rash include:
- Henoch-Schönlein purpura: Which is a type of immune-mediated vasculitis that occurs in infants and young children.
- Urticarial vasculitis: Which is an exaggerated form of an allergic condition.
- Exercise induced vasculitis: Which is a harmless condition affecting females aged 50 years old or more following intense physical exercise.
- Cutaneous polyarteritis nodosa: Which is an immune mediated inflammation of the small and medium-sized blood vessels and usually follow an infection by hepatitis viruses or HIV.
Are bruises dangerous?
Bruises in themselves are not dangerous. They are actually a physiological response of a well-perfused skin and an effective hemostatic blood clotting mechanism. In fact, dead people do not bruise, and the last bruise can be used to determine the time of death -along with other 100 or so forensic signs-, therefore the mere presence of bruises should not call for concern. The cause of bruising, however, can be dangerous or life-threatening either due to excessive bleeding elsewhere in the body or because of other systems or organs that the disease hits. Easy bleeding or bruising can be caused by the following:
1) Defects in platelets:
Our platelets are the first line of defence against us “bleeding until death”. When you injure a blood vessel, the smooth lining covering its inner surface becomes rough and platelets recognize that. The small cellular fragments stick to the exposed part and to themselves forming a “plug” that enlarges in size until it fills as much of the defect as possible to prevent further leakage.
Platelets are formed in the bone marrow from large mother cells called megakaryocytes. They then exit from the bone marrow and circulate for an average of 7 days before being disposed of and replaced. Normal platelet count in a healthy individual is 150,000-450,000 per cubic microliter.
- Low platelet count: If platelet count drops below 150,000 per cubic microliter, controlling even minor leakage from blood vessels becomes difficult. Furthermore, if the platelet count drops beyond 50,000 per microliter, the incidence of life-threatening hemorrhage becomes high especially into the brain.
- Abnormal platelets: In order for platelets to carry out their function properly, they need proper adhesion to the surface and aggregation over one another. In some cases, and due to drugs or inherited abnormalities, this is lost. So, even though platelet count is normal, platelets may still have difficulties performing their normal functions. The collective term for such a disorder is thrombasthenia.