Excessive Sweating
Under normal conditions, 800mL of water is lost daily as insensible loss, mostly in sweat. Excessive sweating can at least double this figure. As a symptom, it is normally part of a package of other problems – it is unusual for the patient to present with excessive sweating in isolation.
Differential diagnosis
Common Diagnoses
- Menopause
- Anxiety
- Infections (Common, Acute)
- Hypoglycaemia: May be Reactive (i.e. Non-Diabetic)
- Hyperthyroidism
Occasional Diagnoses
- Drugs: Alcohol, Tricyclic Antidepressants, Pilocarpine
- Alcohol and Drug Withdrawal
- Shock/Syncope
- Intense Pain
- Hyperhidrosis
- Other Infections (e.g. TB, HIV, Endocarditis, Brucellosis, Lyme Disease)
Rare Diagnoses
- Dumping Syndrome (e.g. Post Gastric Surgery)
- Malignancy (e.g. Lymphoma)
- Organic Nerve Lesions: Brain Tumours, Spinal Cord Injury (Sweating is Localised to Dermatome Involved)
- Pachydermoperiostosis: Localised to Skin Folds of Forehead and Extremities
- Hyperpituitarism/Acromegaly
- Rare Vasoactive Tumours: Phaeochromocytoma, Carcinoid
- Connective Tissue Disorders
Ready reckoner
Key distinguishing features of the most common diagnoses
| Menopause | Anxiety | Infection | Low Glucose | Hyperthyroid | |
|---|---|---|---|---|---|
| Short History | No | No | Yes | Yes | No |
| Vasoconstricted Skin | No | Possible | Possible | Yes | Possible |
| Raised Body Temperature | No | No | Yes | No | No |
| Confusion | No | No | Possible | Possible | No |
| Systemically Unwell | No | No | Yes | Yes | Yes |
Possible investigations
Likely: FBC, ESR/CRP, TFT.
Possible: FSH/LH, LFT, glucose.
Small Print: Autoimmune screen, CXR, tests for uncommon infections, 24 h urinary 5-HIAA, 24 h urinary-free catecholamines and VMAs, CT/MRI scan.
- FBC/ESR/CRP: ESR/CRP and WCC raised in infection. Raised ESR/CRP and anaemia possible in lymphoma and other malignancies.
- TFTs: May reveal thyrotoxicosis as a cause of chronic sweating.
- Glucose: In reactive hypoglycaemia only useful at the time of the sweating.
- FSH/LH: Helps if diagnosis of menopause in doubt.
- LFT: May reveal high alcohol intake.
- CXR might reveal occult infection (especially TB) or malignancy.
- Tests for uncommon infections (e.g. blood test for HIV or Lyme disease, echocardiography for endocarditis).
- Autoimmune screen: May help in confirming diagnosis of connective tissue disease.
- 24 h urinary 5-HIAA: If carcinoid syndrome suspected.
- 24 h urinary-free catecholamines and VMAs: If phaeochromocytoma suspected.
Top Tips
- Length of history is very helpful – short-term sweating is likely to have an apparent, acute cause; if long-term, the diagnosis is more likely to be constitutional or anxiety; in the medium term, the differential diagnosis is much wider.
- Anxiety rarely causes night sweats.
- Do not underestimate the potentially devastating effect of hyperhidrosis.
Red Flags
- Lack of fever does not exclude infection. In some infections (e.g. TB, brucellosis) – and lymphoma – sweating can be out of phase with fever.
- If the problem is persistent, a full examination is advisable, paying attention to the lymph nodes, liver and spleen. If no cause is apparent, have a low threshold for investigations or referral, particularly if the patient is unwell or losing weight.
- Consider unusual infections in the recently returned traveller (e.g. TB, typhoid).
- Episodic skin flushing (especially provoked by alcohol) with diarrhoea and breathlessness is likely to be caused by anxiety – but don’t forget carcinoid syndrome as a rare possibility.