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 is not a disease per se but is indicative of an underlying cause of bleeding.

When purpura spots are very small (<1cm in diameter), they are called petechiae or petechial haemorrhages. Larger, deeper purpura are referred to as ecchymoses or bruising.

Purpura may occur with either normal platelet counts (non-thrombocytopaenic purpuras) or decreased platelet counts (thrombocytopaenic 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.

Examination

It may seem unusual to place examination before history but there is some logic to 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 the nature of the lesions - size, confluence, associated blisters (and what these contain: exudate, blood, pus).
• Where are the lesions? For example, localised lesions may be caused by trauma whereas purpura due to venous hypertension will be in the lower legs with a distribution as shown below.
  
  
• Don't forget to ask/look for lesions in the mucous membranes.
• Tenderness may suggest an inflammatory process.

History

• 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? 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.
• Has general easy bruising been noticed?

Other components of a routine history should be gone through (past medical history, medical and allergic history - including any over the counter drugs - and social history are all relevant)

Review

Having inspected the skin and taken a history, it may be useful to return to a physical examination to re-assess the rash and carry out a further systemic examination looking for hepato-/splenomegaly or neurological signs for example. Be guided by your findings so far.

Purpura is a sign rather than a diagnosis and a cause must be sought. It is helpful to classify causes into vascular (non-thrombocytopaenic) and thrombocytopaenic disorders.

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 leukocytopaenia. 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.

These have been outlined in the differential diagnosis. Here are some points you may wish to bear in mind.

Bacterial infections

Those that cause purpuric rashes include meningococcal septicaemia, streptococcal septicaemia and diphtheria. Several acute viral infections also cause purpuric rashes. These include smallpox, chickenpox, measles, parvovirus B19 and haemorrhagic fevers caused by Ebola virus, Rift valley virus and Lassa fever.

Allergic vasculitic purpura

This 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-Schönlein 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.

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.

Strong steroids

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.

Blood transfusions

Severe thrombocytopaenia 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

Pigmented purpuric dermatoses

These are a group of diseases characterised by erythrocyte extravasation - particularly in the lower limbs, associated with haemosiderin deposition. Think of these in chronic cases.

Amyloid

Both primary and secondary amyloid can cause purpura that is known as "pinch-purpura" because of the typical appearance on the cheeks.³

Factitial purpura

This may be considered where there are episodes of inexplicable bleeding/bruising. They may represent severe emotional or psychiatric disturbance. They may also be a sign of abuse.

• 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.