Aquagenic pruritus is a condition in which contact with water of any temperature causes intense itching without any visible skin changes. The symptoms may begin immediately after contact with water and can last for an hour or more.
The symptoms of the condition are similar to those seen in patients with other conditions; therefore, a thorough evaluation should be performed to rule out other more serious conditions. Aquagenic pruritus causes intense itching in the parts of the body that come in contact with water. The legs are most frequently affected, followed by the arms, chest, back, and abdomen. More rarely, the head, neck, face and hips may be affected The palms, soles, and mucosa are usually not affected. Because aquagenic pruritus may be one symptom of polycythemia vera or another condition, it is important to look for problems in other parts of the body to rule out these conditions.
The cause of aquagenic pruritus is unknown; however, familial cases have been described. In some cases, it is a symptom of polycythemia vera or other underlying conditions such as myeloproliferative neoplasms or myelodysplastic syndromes; hypereosinophilic syndrome; or juvenile xanthogranuloma. Aquagenic pruritus may precede a diagnosis of polycythemia vera by several years or more. Other conditions that reportedly may induce aquagenic pruritus include lactose intolerance and hepatitis C.
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
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 in which the cause is unknown (i.e not known to be associated with polycythemia vera or another condition). Earlier publications have cited a positive family history in 33 % of affected individuals. However, to our knowledge, no gene proven to be responsible for aquagenic pruritus alone has been identified, and the exact risk for a family member of an affected person to develop the condition is not known.
No definitive medical test is known for aquagenic pruritus. Rather, the diagnosis is made by excluding all other possible causes of the patient's itching. Since pruritus is a symptom of many serious diseases, it is important to rule out other causes before making a final 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; and
- Exclusion of all physical urticarias, symptomatic dermographism, and polycythemia vera, as well as other diseases that my have aquagenic pruritus as a symptom.
Overall, treatment is a challenge. Since the cause of the condition cannot be fully avoided in all cases, treatment is usually focused on topical itch management. This can be effected by the application of antipruritic lotions or creams, using phototherapy, or the application of hot or cold packs to the skin after water contact. Paradoxically, hot baths or showers help many patients, possibly because heat causes mast cells in the skin to release their supply of histamine and to remain depleted for up to 24 hours afterward. However, the itching associated with aquagenic pruritis is not clearly caused by histamine; other neurotransmitters, such as substance P, may be involved.
Treatments can include applying capsaicin cream on the affected areas, and filtered Ultraviolet-B Phototherapy in a hospital or health clinic, often using a vertical light cubicle in which the patient stands for the exposure duration. Some people utilize tanning beds to accomplish such treatment, but skin cancer can become a concern for frequent tanning due to the broader UV spectrum of the beds.
Antihistamines, PUVA therapy and various medications have been tried with varying success. H1 and H2 blockers, such as loratadine, doxepin, or cimetidine, have historically been the first line of pharmacological treatment, but not all sufferers find relief with these medications. When antihistamines do work, loratadine seems to be the most effective for mild cases and doxepin most effective for more severe cases. Naltrexone, hydrocortisone, or propranolol may relieve itching for some people.
It is difficult to find effective treatments for aquagenic pruritus because the underlying cause is not well understood. Numerous treatments have been tried (both nonpharmacologic and pharmacologic), with varying success among individual patients. Therapies that have been used include:
- Topical capsaicin
- Adding sodium bicarbonate to bath water
- Selective serotonin reuptake inhibitors
- UVB phototherapy
- PUVA therapy
People with questions about the management of aquagenic pruritus should speak with their doctor about the treatment options available.