The patient
This 30-year-old man turned up, somewhat apologetically, in the afternoon emergency clinic.
‘I know it's not really urgent,' he said. ‘I just want to make sure it's not catching.'
The rash had first appeared a couple of days previously and had rapidly developed into the florid lesions he showed me.
He had no relevant medical history and was on no regular medication – though he had taken some ibuprofen for what sounded like an upper respiratory tract infection a week or two previously.
The rash didn't itch, and he felt perfectly well in himself.
First instinct
Although the rash was quite impressive – with extensive, well-defined erythematous and slightly scaly lesions over his trunk – my reflex response was to label this as viral because I'd spent much of the afternoon seeing viral children, many of whom had non-specific rashes.
Perhaps it was linked to his recent URTI, or was the first sign of a new infection.
Because he'd only had the rash for a couple of days the possible differential was wide, though – as I explained to him – the viral hypothesis would be backed up if it resolved about as quickly as it had appeared.
Differential diagnosis
- Viral
- Drug reaction
- Guttate psoriasis
- Pityriasis rosea
- Lichen planus.
I thought about the fact that he had taken ibuprofen. NSAIDs are a fairly common cause of skin reactions, though if this was the cause, it seemed unusually delayed.
Guttate psoriasis was certainly a possibility, given the appearance. He'd mentioned a preceding viral-type illness, but I hadn't thought to enquire further. It would have been interesting to know if he'd meant a severe sore throat, because a streptococcal infection can trigger this form of psoriasis.
Pityriasis rosea is something we see more commonly than guttate psoriasis, and the
slight scale is characteristic. But these lesions looked more florid than those seen in most cases of pityriasis rosea, and he hadn't reported the typical ‘herald patch'.
The only other differential, on the basis of the appearance, was lichen planus. This seemed unlikely, though, given the extensive distribution, the sudden onset and the lack
of itch.
The hidden clue
The main giveaway was the fact that two weeks later he was back, with the rash as bad as ever.
This effectively scrubbed a viral infection and a drug reaction off the list of possibilities – which meant that guttate psoriasis was now the prime suspect.
This was supported when I expanded the history to uncover the previously hidden clue that a couple of weeks previously his ‘virus' had consisted of a really nasty sore throat, with a fever.
Getting on the right track
The icing on the cake was the fact that, although he had never suffered psoriasis himself, his father had. Other than reassurance, the only treatment required was some emollient – and within about six more weeks his guttate psoriasis had resolved.
Dr Keith Hopcroft is a GP in Laindon, Essex
