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Snapshot diagnosis - what's that purple rash?

Dr Mike Wyndham was right in his initial diagnosis of this unusual case, but not sure as to the cause.

Dr Mike Wyndham was right in his initial diagnosis of this unusual case, but not sure as to the cause.

The patient

This eight-month-old baby had had a difficult start to her life. She had suffered from two bouts of pneumonia but responded well to antibiotics. However, she had developed this purplish coloured rash, which was fixed and did not improve when she was warm. Also, her weight was faltering.

First instinct

My initial thought was that this was livedo reticularis.

Possible underlying causes

There was no doubt about the diagnosis, but what was uncertain was the cause. The usual causes of livedo reticularis are:

• physiological as a reaction to a cold environment

• increased blood viscosity caused by conditions such as polycythaemia, presence of cryoglobulins

• Sneddon's syndrome – the presence of anticardiolipin antibodies in cerebrovascular disease

• vasculitic conditions such as polyarteritis nodosa, systemic lupus erythematosus.

Getting on the right track

The rash was fixed regardless of temperature, which excluded a physiological cause. All the other above conditions would be associated with older age groups.

At the follow-up appointment I was still concerned about the continuing rash and faltering weight and so arranged another appointment with the paediatrician who did further tests. A positive HIV test was the result of one of them. Her mother was found to be HIV positive too.

Dr Mike Wyndham is a GP in Edgware, north London

What's that purple rash?]]>

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