Idiopathic aquagenic pruritus: pathogenesis and effective treatment with atenolol

Aquagenic pruritus (AP) is a rare condition with unknown pathogenesis. We explored its pathogenesis through investigations of a patient and report the first case to be effectively treated with atenolol. A 36-year-old Indian female presented with idiopathic AP. Small-fiber neuropathy involving itch/pain-transmitting C-fibers appears to be pathogenetically important: compared with matched controls, our patient had increased intra-epidermal nerve fibers, raised warmth detection threshold, and marked hyperknesis to electrical stimulation. Autonomic nerve function tests and fingertips vasoconstriction response were normal, indicating integrity of other small (Aδ and C) nerve fibers. She was initially treated with propranolol with good response, but was subsequently switched to atenolol for convenient once-a-day dosing. Symptoms were well controlled long term with no side effect experienced. Atenolol may exert its effect in AP through blockage of over-activated neuronal sodium channels. Through the investigations, we propose that the pathogenesis of idiopathic AP may involve the following: upon contact of the skin with water, yet-unknown mediator/s released stimulate dysfunctional and hyper-innervated C-nerve fibers, which may have resulted from a sodium channel defect. Atenolol may be a preferred therapeutic option compared with propanolol, in view of its convenient once-a-day dosing and better side effect profile.