Aquagenic pruritus

The underlying cause of aquagenic pruritus is unknown. In some cases, it is a symptom of polycythemia vera or another underlying condition. Aquagenic pruritus may precede a diagnosis of polycythemia vera by several years or more. Other conditions associated with aquagenic pruritus include myeloproliferative neoplasms or myelodysplastic syndromes, hypereosinophilic syndrome, and juvenile xanthogranuloma. Lactose intolerance and hepatitis C may also induce aquagenic pruritus.

Drug-induced aquagenic pruritus has been reported in patients treated with clomipramine (a tricyclic antidepressant), bupropion (prescribed for smoking cessation), and hydroxychloroquine and chloroquine (antimalarial drugs also used for rheumatoid arthritis and lupus).

Possible underlying causes of aquagenic pruritus that have been proposed include:

• increased mast cell degranulation - release of granules rich in histamine and other compounds into the body by mast cells, a special type of cell that plays a role in the immune system
• increased circulating histamine
• release of acetylcholine - a chemical in the body which sends signals from nerves to muscles and between nerves in the brain
• increased skin fibrinolytic activity - activity that controls clot size by promoting the breakdown of clots

There is no specific exam that confirms a diagnosis of aquagenic pruritus. The diagnosis is generally made by ruling out other conditions. The following criteria may help to make the diagnosis:

• Severe itching (may be the only symptom), prickling, stinging, or burning that consistently develops after skin contact with water, regardless of water temperature or salinity
• Lack of visible skin manifestations
• Reaction within minutes of exposure and lasting anywhere between 10 minutes to 2 hours
• Lack of another skin disease, underlying condition, or medication to account for the reaction
• Exclusion of all physical urticarias, symptomatic dermographism, and polycythemia vera, as well as other diseases that my have aquagenic pruritus as a symptom.

While the underlying cause of aquagenic pruritus is unknown, there has been evidence that genetic factors may play a role in the condition. Familial cases have been reported, particularly in cases of unknown cause (i.e not associated with polycythemia vera or another condition). However, to our knowledge, no gene proven to be responsible for aquagenic pruritus alone has been identified, and the risk for a family member of an affected person to develop the condition is not known.

It is difficult to find effective treatments for aquagenic pruritus because the underlying cause is poorly understood. Therapies that have been attempted with varying success include:

• Antihistamines
• Analgesics (pain relievers)
• Opioid receptor antagonists
• Alpha interferon 2b
• Cholestyramine
• Clonidine
• Topical capsaicin cream
• Naltrexone
• Adding sodium bicarbonate to bath water
• Selective serotonin reuptake inhibitors
• UV therapy - shown to be effective in about 50% of patients
• PUVA therapy
• Propranolol
• Atenolol
• Using baby oil or other hydrophobic emollients (skin softeners that repel water) before and/or after showering

People with questions about the management of aquagenic pruritus should speak with their doctor about available treatment options.