Key distinguishing features of the most common diagnoses
|Contact Allergy||Scabies||Atopic Eczema||Pityriasis Rosea||Psoriasis|
|History of Chemical Exposure||Yes||No||Possible||No||No|
|Worse at Night||No||Yes||Possible||No||No|
|Mainly on Flexures||No||No||Yes||No||No|
|Mainly on Extensor Surfaces||Possible||No||No||No||Yes|
Possible:Urinalysis, blood glucose or HbA1c, FBC, ferritin, ESR, U&E, LFT, TFT.
- Urine: Dipstick for glycosuria (blood glucose or HbA1c if positive).
- FBC, ferritin: Will reveal iron-deficiency anaemia and polycythaemia; eosinophil count may be raised in allergic conditions; WCC may be very high in leukaemia; ESR may be elevated in lymphoma; low ferritin will confirm iron deficiency.
- U&E: Will reveal uraemia.
- LFT: Deranged liver enzymes and raised bilirubin in liver disease. Abnormalities here will require further investigations or referral.
- TFT: Both hypo- and hyperthyroidism can lead to skin changes which cause itching.
- The key to sorting out this symptom is to identify whether or not there is an underlying rash. Itching with a rash depends on identifying the rash; itching without a rash (other than that caused by scratching) depends on identifying any systemic cause.
- An itchy, unidentifiable rash which is worse at night is likely to be scabies, particularly if any contacts are affected.
- Warn the patient that scabies treatment may take a week or two fully to relieve symptoms – otherwise, the patient may apply the treatment repeatedly, causing a chemical irritation and diagnostic confusion.
- The books usually state that psoriasis doesn’t itch – but it certainly can, so don’t let this symptom put you off the diagnosis.
- It is usually very difficult to identify the allergen in a single episode of urticaria (and, indeed, the cause may not be allergic at all). Tell the patient to keep a note of foods or medicines just ingested so that, in the event of recurrence, any culprit can be identified.
- If no obvious cause, always examine the abdomen and lymph nodes – do not miss lymphadenopathy, or enlarged liver, spleen or kidneys.
- Don’t be tempted not to examine the itchy, malodorous self-neglected patient – poor personal hygiene may deceptively mask some other identifiable underlying cause.
- Beware of apparently florid eczema appearing for the first time in an elderly patient – this may be a manifestation of serious underlying pathology.
- Don’t forget iatrogenic causes – enquire about any drugs recently prescribed.