Itching
Differential Diagnosis
Common Diagnoses
Occasional Diagnoses
- Urticaria (Various Causes)
- Liver Disease
- Iron Deficiency, with or without Anaemia
- Renal Failure (Uraemia)
- Lichen Planus
- Prickly heat
- Drug Side Effect (with or without Rash)
- Simple Pruritus: no Cause Found (Especially in Elderly Where it May Simply be Caused by Dry Skin)
- Diabetes Mellitus
- Hyperthyroidism
- Hypothyroidism
Rare Diagnoses
- Herpes Gestationis
- Dermatitis Herpetiformis
- Psychogenic (Includes Dermatitis Artefacta)
- Leukaemia and Myeloproliferative Disorders
Ready Reckoner
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 |
| Widespread Itch | Possible | Yes | Possible | Yes | 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 Investigations
Likely:None.
Possible:Urinalysis, blood glucose or HbA1c, FBC, ferritin, ESR, U&E, LFT, TFT.
Small Print:None.
- 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.
Top Tips
- 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.
Red Flags
- 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.