Purpura means purple. A purpuric rash usually results from bleeding into the skin from small blood vessels. Although a purpuric rash is most obvious on the skin, it can occur on any body surface, including the lining (mucous membrane) of the mouth and on body organs.
What are the symptoms?
There are many wonderful things associated with the colour purple. Think purple flowers, purple grapes and Purple Rain, Purple Rain. Unfortunately, when it comes to skin rashes, purple is not so great. It usually means small spots of blood have leaked into the skin. It's easy to tell if you have a purpuric rash rather than another spotty rash because if you press on the skin with an empty drinking glass the spots won't fade.
Depending on the cause, you may notice other odd things happening like joint pains, fevers or tummy pains. Because so many conditions can cause a purpuric rash, I could devote the rest of this leaflet to all the possible symptoms that you may notice. This would be immensely boring for all of us, so I won't even try.
Read more about the symptoms of purpuric rashes.
What are the causes?
Now we are getting to the meaty part. Causes of purpura have conveniently divided themselves into two groups depending on the platelet count (platelets are tiny blood cells that help your blood to clot). Purpura can be caused by conditions in which the platelet count is normal (non-thrombocytopenic) and those in which it is low (thrombocytopenic).
Non-thrombocytopenic causes can be further divided into:
- Those you were born with such as various inherited causes (for example, Osler-Weber-Rendu syndrome - try memorising that to impress your friends) and viruses caught from your mum while you were in the womb.
- Those you acquired after you were born (for example, severe infections, allergies, reactions to medicines).
Thrombocytopenic causes can be divided into:
- Those caused by bone marrow failure (for example, leukaemia).
- Those causing increased breakdown of platelets (for example, immune thrombocytopenia, viruses again).
- Those affecting the blood clotting system (for example, disseminated intravascular coagulation).
- Other rare causes (for example, rapid blood transfusion).
Learn more about the causes of purpuric rashes.
How is it diagnosed?
Expect the doctor to ask you lots of questions. They are not being nosy but may genuinely need to know an awful lot about your health, the sort of medicines you sneak into your local pharmacy to buy and your lifestyle. They may also ask you about any recent travel abroad. Unfortunately, what happens in Benidorm, doesn't always stay in Benidorm.
The doctor will have a look at your rash and probably do a quick all-round examination. At this point they will hopefully look less puzzled than they did at the beginning of the consultation. They will then slowly and with great dignity place their hands on the computer keyboard, the better to produce reams of blood test request forms. The good news is that usually a hundredweight of these forms still only equates to one needle in the arm. You will most likely have a full blood count, a liver function test and tests of your immune system. You may need some other fancy tests, depending on what your doctor is looking for.
Find out more about the diagnosis of purpuric rashes.
How is it treated?
How long is a piece of string? The treatment will depend on the cause and we would find a list of possible treatments even more boring than a list of possible symptoms.
The outlook (prognosis) depends on the cause and there isn't always an easy answer to some of the underlying conditions. If there isn't an effective cure, you may have to resign yourself to living with the rash.
There's just one treatment that all patients with purpuric rash have if their platelet count is very low and that's a platelet transfusion. If that happens you'll be a pretty rare and special person. You might as well buy a lottery ticket. It's called karma.
Read more about the treatment of purpuric rashes.
What are the symptoms of a purpuric rash?
A purpuric rash is not a disease but it is caused by conditions that result in blood leaking into the skin and other body surfaces.
The rash looks like little red spots on the skin. It's easy to recognise because - unlike other spotty rashes - the spots don't fade when you press them. The best way to do this is with a drinking glass or other see-through object like a plastic ruler.
There are so many different causes of a purpuric rash it's difficult to list all the symptoms that may occur due to the underlying illness. However, common symptoms you may notice occurring with the rash include:
- Spots inside the mouth.
- Blisters (which may be clear or yellow like little boils).
- Tenderness in the area of the rash.
- A high temperature (fever).
- Feeling under the weather.
- Joint pains.
- Tummy pains.
What causes a purpuric rash?
There are many different causes of purpuric rashes. Several of them can be grouped into those caused by lack of platelets and those in which the platelets are present in normal numbers. Conditions in which the platelet numbers are normal are called non-thrombocytopenic. Those in which the platelet numbers are low are called thrombocytopenic.
- Conditions you are born with, such as:
- Osler-Weber-Rendu syndrome.
- Ehlers-Danlos syndrome.
- Pseudoxanthoma elasticum (a condition affecting the elastic tissue of the blood vessels and other parts of the body).
- Infections picked up during pregnancy whilst still in the womb, such as cytomegalovirus and rubella.
- Conditions acquired after you were born, such as:
- Severe infections such as sepsis, infection with one of the germs that cause meningitis (meningococcus).
- Allergy-based conditions such as Henoch-Schönlein purpura.
- Disorders of the connective tissue that connects and binds other bits of the body together, such as systemic lupus erythematosus and rheumatoid arthritis.
- As a side effect of medicines such as steroids and sulfonamides (antibiotics).
- Other causes, such as ageing of the skin, injury (trauma), lack of vitamin C (scurvy) and poor blood supply, especially to the legs.
- Conditions resulting from problems with platelet production, such as:
- Bone marrow failure - for example:
- Conditions that increase the breakdown of platelets, such as:
- Immune thrombocytopenia.
- Systemic lupus erythematosus.
- Viral infections.
- Conditions affecting the blood clotting (coagulation) system, such as:
- Disseminated intravascular coagulation which causes excessive blood clotting in small blood vessels).
- Haemolytic uraemic syndrome (destruction of blood cells associated with kidney problems).
- Enlarged spleen.
- Conditions causing dilution of the platelets, such as rapid transfusion of large quantities of stored blood.
How is a purpuric rash diagnosed?
Because there are so many causes, diagnosing the reason why you have developed a rash takes a bit of detective work. The doctor will need to ask you questions about the rash and your general health (take a history), examine you and do some tests.
What questions will I be asked?
The sort of questions the doctor will ask you may include:
- How long you've had the rash.
- Whether it's changed over time.
- Whether you bruise easily.
- Whether you've been abroad recently.
- Whether you've recently taken any medicines you've bought from a pharmacy.
- If this is not your regular GP:
- Whether you've had any illnesses in the past or have any long-term conditions.
- What prescribed medicines you are taking.
- Whether you have any allergies.
- Questions about your lifestyle (drinking, smoking, etc).
What will the doctor be looking for?
Examination of your rash and general body systems may give a clue as to the cause. The doctor will be looking for:
- The size of the spots, whether they run together, whether there are any blisters (and whether they are filled with clear fluid, blood or pus).
- Tenderness of the spots (this can happen with diseases causing inflammation, such as rheumatoid arthritis).
- Any spots inside your mouth.
- The location of the spots - for example, spots close together in one area are often seen where there has been injury, whereas spots on both lower legs suggest s problem with the circulation in your veins, as in the picture below:
- Swollen organs in your tummy, such as an unusually large liver or spleen.
- Numbness, weakness or other unusual features on examining your nervous system.
Will I need any tests?
There are a huge number of tests which could be arranged, but hopefully by the time the doctor has taken your history and examined you they will have a reasonable idea as to which are the most important. Most tests can be done on blood samples and may include:
- A full blood count to check your platelets, white cells and red cells.
- Inflammatory markers (tests to check for inflammation).
- Tests to check how well your liver is working.
- Tests to check your blood clotting system.
- Tests to check for unusual levels of protein in your blood.
- Tests to check for proteins that attack the body's own cells (autoantibodies).
Other tests may be ordered depending on the suspected cause. For example, you may need a blood culture if your doctor thinks you have an infection, or a lumbar puncture if they think you have a nervous system disorder.
How is a purpuric rash treated?
The treatment will depend on the cause. Leaflets on the specific conditions mentioned in the Causes section will give you more details. If your platelet count is very low, the first treatment you will receive will be a platelet transfusion.
Further reading & references
- Purpura; University of Maryland Medical Centre
- Maher GM; Immune thrombocytopenia. S D Med. 2014 Oct;67(10):415-7.
- Purpura; Internal Medicine Reference
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Laurence Knott
Prof Cathy Jackson