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By Professor Paul Rutter, University of Portsmouth
Hypothesis generation
Non-blanching/purpuric rashes result from haemorrhage from small blood vessels into the dermis. A cardinal sign of a purpuric rash is that it does not blanch on pressure, unlike other types of rashes.
Depending on the size of the individual lesions they can be defined as:
- Petechiae (<5mm diameter), or
- Purpura (5-10mm diameter), or
- Ecchymoses (>1cm diameter).
Possible causes
There are a number of causes of non-blanching rash, including thrombocytopenia, platelet dysfunction, disorders of coagulation, and loss of vascular integrity. Meningitis is still a priority for exclusion when considering the differential diagnoses despite a significant decline in meningococcal disease due to childhood vaccination. Most non-blanching rashes will not be a sign of meningococcal disease.
Likely diagnoses
- Medicines
- Viral meningitis
Possible diagnoses
- Forceful coughing/vomiting
- Haemolytic uraemic syndrome
- Henoch-Schönlein purpura (HSP)
- Idiopathic thrombocytopenic purpura (ITP)
- Medicine-induced meningitis
- Non-accidental injury
- Senile purpura
Critical diagnoses
- Acute leukaemia
- Aplastic anaemia
- Bacterial meningitis
Key points
- Caused by small bleeds beneath the skin
- Mostly caused by conditions that are non-serious
- Any person with rapid progression/deterioration of symptoms needs urgent referral to A&E
Continued information gathering
The first step in forming a diagnosis is to examine the rash. You inspect the child’s legs and observe a widespread macular rash mainly below the knees that is red/purple in colour. When you press the rash it does not blanch, so it is a purpuric rash.
The age of the child is also helpful in shaping your thinking. Besides meningitis, ITP and HSP are more commonly seen in this age range compared to infants where congenital bleeding disorders and leukaemia need to be considered.
It is reassuring that the child appears to be well, as a short acute illness raises the suspicion of sepsis. You ask the parents about her general health. They say she seems fine but has complained a little of a tummy ache.
Her relatively good health suggests you are not dealing with meningitis despite the rash. You do, however, ask if she is up to date with all her immunisations, and her parents confirm that she is. This helps to rule out the possibility of bacterial meningitis.
Problem refinement
Her symptoms fit with HSP – lower limb rash and abdominal pain. Although joint pain is common in HSP, it is absent in this patient. HSP often follows recent infection, so you ask the parents if she has had any coughs or colds over the last few weeks. They tell you she had a cough a couple of weeks ago but it cleared up last week.
HSP seems, at this stage, the most likely diagnosis given the parents have not reported any other bleeding symptoms (this would suggest ITP).
Assessment
As part of your examination should:
- Observe the distribution of the rash, as well as the symmetry, shape, size, and colour
- Assess the configuration of the lesions (e.g. discrete, confluent)
- Note the texture (e.g. smooth, blisters, rough or scabs), and any temperature difference on palpation.
It is important to note that skin rashes can be more difficult to assess and in people with skin of colour.
As part of the medical history, you should ask:
- When it started, how it has spread and the speed of development
- How it feels (e.g. itchy, hot or painful)
- About any other signs and symptoms (e.g. fever, nausea, skin colour changes)
- About any known medical conditions, or current medications, or any treatment they have tried.
- About any family history of dermatological conditions.
- About and relevant occupational or social history (e.g. hobbies).
Red flags
The main concern is a child who appears systemically unwell. We know this patient is generally well.
Management
Self-care options
None.
Prescribing options
The condition is self-limiting. However, to fully exclude other causes, a full blood count could be arranged to detect thrombocytopaenia.
Safety Netting
You reassure the parents that the rash is not meningitis, and you believe it is HSP that has probably been triggered by a recent infection. You tell them you cannot confirm the diagnosis as a blood test is needed to rule out other causes. A blood test is arranged.
Now check your understanding of non-blanching rash by answering the following questions:
1. A 4-year-old child presents with lethargy, fever and a rapidly spreading non-blanching purpuric rash. He also has delayed capillary refill time. Which ONE of the following investigations would be most appropriate?
-
Blood cultures
-
CT scan
-
Coagulation screen
-
Lumbar puncture
-
Serum ferritin
2. A patient presents with a non-blanching rash and epistaxis. Blood results show thrombocytopenia. Which ONE of the following is the most likely diagnosis?
-
Acute leukaemia
-
Henoch–Schönlein purpura
-
Immune thrombocytopenic purpura (ITP)
-
Medicine-induced
-
Meningococcal septicaemia
3. A patient presents with a non-blanching rash and severe abdominal and joint pain. Which ONE of the following is the most likely diagnosis?
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Acute leukaemia
-
Aplastic anaemia
-
Bacterial meningitis
-
Henoch–Schönlein purpura
-
Viral meningitis
4. A 74-year-old man presents with a non-blanching purpura on the lower limbs. He takes warfarin for AF. Which ONE of the following is the most likely?
-
Excess anticoagulation
-
HSP
-
Thrombocytopenia
-
Senile purpura
-
Vitamin C deficiency
5. A young adult presents with non-blanching rash, fever, myalgia, and a history of recent antibiotic use. Which ONE of the following is the most likely diagnosis?
-
HSP
-
ITP
-
Medicine-induced
-
Meningococcal sepsis
-
Viral meningitis
Answers: 1 A; 2 C; 3 D; 4 A; 5 C
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