Purpuric Rashes

Purpura is a purplish discoloration of the skin produced by small bleeding vessels near the surface. Purpura may also occur in the mucous membranes, especially of the mouth and in the internal organs.

Purpura per se is indicative of an underlying cause of bleeding.

When purpura spots are very small, they are called petechiae or petechial haemorrhages. Large purpura are called ecchymoses or bruising.

Purpura may occur with either normal platelet counts (nonthrombocytopenic purpuras) or decreased platelet counts (thrombocytopenic purpuras). Platelets help maintain the integrity of the capillary lining as well as being important in the clotting process. As a general rule, purpura indicates a problem of the platelet system whilst a deficiency of clotting factors will cause haematomas or haemarthrosis as in haemophilia. Nevertheless, clotting factor deficiency must be considered.

The appearance of purpura is quite characteristic and it does not blanche on pressure.

History

It may seem unusual to place examination before history but there is some method in this. In reality, the patient is likely to start the consultation by presenting the rash and so inspection of the rash and noting such matters as the general condition of the patient will occur at the outset. Note also the distribution of the rash. Purpura due to venous hypertension will be in the lower legs with a distribution as shown in the picture above.

• Note the age of the patient. Henoch-Schonlein purpura tends to occur in children. Senile purpura is confined to the elderly. Leukaemia and myeloproliferative disorders can occur at any age.
• How long has the rash been present? Is it changing noticeably? Meningococcal septicaemia will be very recent in origin and changing almost visibly.
• Is the patient otherwise well?
• Has general easy bruising been noticed?

If a child has developed a purpuric, possibly meningococcal rash, but does not seem unwell, do not be lured into a false sense of security. That child may be moribund just 20 minutes later.

Having inspected the skin and taken a history, it may be useful to return to abdominal examination as some of the causes may produce splenomegaly and perhaps hepatomegaly too. As mentioned in abdominal examination, a spleen has to be at least twice its normal size to be palpable.

Purpura is a sign rather than a diagnosis and a cause must be sought.

Purpura can be divided into two group:

• Thrombocytopenic purpuras
• Non-thrombocytopenic purpuras

Causes of thrombocytopenic purpuras include:

• Idiopathic thrombocytopenia purpura
• Low platelet count in leukaemia and myeloproliferative diseases or drugs that suppress the bone marrow
• Platelet consumption can occur with a large haemangioma of disseminated intravascular coagulation
• Meningococcal septicaemia

Causes of non-thrombocytopenic purpura include:

• Vasculitis such as Henoch-Schonlein purpura
• Congenital cytomegalovirus and congenital rubella
• Dependent purpura with venous hypertension
• Senile purpura
• Steroid induced purpura
• Adverse drug reactions in which platelet numbers are normal but function is impaired

These lists are far from exhaustive. Trauma can cause purpura. Vitamin C deficiency (scurvy) tends to produce petechiae rather than purpura. In those at risk, ask about fresh fruit and vegetables in the diet.

This will be guided by the differential diagnosis, much of which will already have been excluded.

• FBC, ESR, platelets. The platelet count is fundamental. Leukaemia or related diseases may produce anaemia and leukocytopenia. ESR may indicate an inflammatory process. It is very non-specific.
• LFTs check for liver disease.
• A coagulation screen will screen for clotting factor deficiencies.
• If the patient is on warfarin, check INR.
• Plasma electrophoresis may show hypergammaglobulinaemia, paraproteinaemia and cryoglobulinaemia.
• Autoantibody screen for connective tissue disorders.

The clinical condition may indicate further investigations, including blood culture and lumbar puncture.

There are a number of other conditions that may be considered:

• Bacterial infections that cause purpuric rashes include meningococcal septicaemia, streptococcal septicaemia and diphtheria. Several acute viral infections also cause purpuric rashes. These include smallpox, chickenpox, measles and haemorrhagic fevers caused by Ebola virus, Rift valley virus and Lassa fever.
• Allergic vasculitic purpura is caused by inflammation and infiltration of the blood vessel wall as an anaphylactic reaction to a number of physical and chemical stimuli, including infections. Henoch-Schonlein purpura is one of the commonest. Is often preceded by a URTI due to β-haemolytic streptococcal infection. It can occur in epidemics in young children with a fever followed by a purpuric rash, that may be slightly raised. Typically, it affects the fronts of the legs and the buttocks. There may be associated acute arthritis, GI pain and nephritis with proteinuria. The rash may continue to form over several weeks. Serious acute complications include CNS bleeding, acute intussusception or acute renal failure. Usually it is a self-limiting condition but it may respond to steroids.
• In disseminated intravascular coagulation (DIC), there is massive ecchymosis with sharp, irregular borders of deep purple colour and an erythematous halo. It can evolve to haemorrhagic bullae and blue-black gangrene. These appear as multiple lesions, often symmetrically involving distal extremities, areas of pressure, lips, ears, nose and trunk.
• Long-term use of strong steroids can cause widespread purpura and bruising normally on extensor surfaces of the hands, arms and thighs. It is caused by atrophy of the collagen fibres supporting blood vessels in the skin. A similar appearance is also found in senile type purpura.
• Platelet activation occurs in haemolytic uraemic syndrome and they are consumed.
• Thrombotic thrombocytopenia purpura can occur.
• Purpuric lesions can often appear in normal patients, usually women. Bruises, either single or multiple, appear spontaneously mainly on arms or legs and resolve without any specific treatment. Senile purpura is usually seen on areas exposed to mild repeated trauma, such as the back of hands. Lesions keep their dark colour often for several weeks and there is no abnormality in bleeding times.
• Both primary and secondary amyloid can cause purpura that is known as "pinch-purpura" because of the typical appearance on the cheeks.¹
• Severe thrombocytopenia 5 to 12 days after receiving a blood product containing platelets is a rare complication, usually confined to multiparous women. It is due to the production of an antibody to a specific platelet antigen that she normally lacks. Patient normally recovers within 1 to 3 weeks but the condition can be lethal and may need treatment with plasmapheresis or IV immunoglobulins.²

• As purpura is a physical finding rather than a disease, the management is to make a diagnosis and to act accordingly. The management of the various diseases is found in the respective articles.
• Purpura usually indicates a platelet count below 30x10⁹/l and a serious haemorrhagic potential. A count of 20x10⁹/l or less requires urgent treatment.
• If a child has bruising, check all over, including the anogenital area. Keep non-accidental injury in mind
• Never give an intramuscular injection if a serious bleeding disorder is suspected or a very painful haematoma will develop.
• The glass test (diascope) is well known to patients and is very useful.