Non-blanching rashes are caused by bleeding under the skin. Petechiae are small (< 3mm), non blanching, red spots on the skin caused by burst capillaries. Purpura are larger (3 – 10mm) non-blanching, red-purple, macules or papules created by leaking of blood from vessels under the skin.
Any child presenting with a non-blanching rash needs immediate investigation for the underlying cause. The most concerning differential is meningococcal septicaemia. Patients with features of sepsis need immediate management for life threatening meningococcal sepsis.
Differential Diagnosis
Meningococcal septicaemia or other bacterial sepsis: This presents with a feverish unwell child. Any features of meningococcal septicaemia indicate emergency management with immediate antibiotics. This can lead to significant morbidity and mortality if treatment is delayed.
Henoch-Schonlein purpura (HSP): This typically presents as a purpuric rash on the legs and buttocks and may have associated abdominal or joint pain.
Idiopathic thrombocytopenic purpura (ITP): This develops over several days in an otherwise well child.
Acute leukaemias: This presents with a gradual development of petechiae, potentially with other signs such as anaemia, lymphadenopathy and hepatosplenomegaly.
Haemolytic uraemic syndrome (HUS): This is associated with oliguria (very low urine output) and signs of anaemia. This often presents in a child with recent diarrhoea.
Mechanical: Strong coughing, vomiting or breath holding can produce petechiae in a “superior vena cava distribution”, above the neck and most prominently around the eyes.
Traumatic: Tight pressure on the skin, for example in non-accidental injury, or occlusion of blood in an area of skin can lead to traumatic petechiae.
Viral illness: This is often the explanation when other causes and serious illness are excluded. Typical causes are influenza and enterovirus.
Investigations
Potentially helpful investigations include:
- Full blood count: Anaemia can suggest HUS or leukaemia. Low white cells can suggest neutropenic sepsis or leukaemia. Low platelets can suggest ITP or HUS.
- Urea and electrolytes: High urea and creatinine can indicate HUS or HSP with renal involvement.
- C-reactive protein (CRP): This is a non-specific indication of inflammation or infection and can be useful but not definitive in excluding sepsis.
- Erythrocyte sedimentation rate (ESR): This is a non-specific indication of inflammatory illness such as a vasculitis (HSP) or infection.
- Coagulation screen, including PT, APTT, INR and fibrinogen can diagnose clotting abnormalities.
- Blood culture: This can be useful but not definitive in diagnosing or excluding sepsis.
- Meningococcal PCR: This can confirm meningococcal disease, although this should not delay treatment.
- Lumbar puncture: To diagnose meningitis or encephalitis.
- Blood pressure: Hypertension can occur in HSP and HUS. Hypotension can occur in septic shock.
- Urine dipstick: Proteinuria and haematuria can suggest HSP with renal involvement, or HUS.
Management
Patients with a non-blanching rash always require urgent referral and investigation unless there is a clear and unconcerning cause. The extent of the investigation depends on the clinical picture. Where there is doubt, patients are usually treated as meningococcal sepsis without waiting for investigations.
Definitive management will depend on the underlying cause.
Last updated January 2020