Chronic pruritus requires careful evaluation for primary dermatologic or systemic causes. In addition to treatment of the underlying cause, when identified, various topical and systemic therapies may be used, although supporting data from randomized trials are scarce. The latest article in our Clinical Practice series comes from Dr. Gil Yosipovitch of Wake Forest University Baptist Medical Center.
Chronic pruritus is associated with markedly reduced quality of life; a recent study demonstrated that chronic itch is as debilitating as chronic pain. Deranged sleep patterns and mood disturbances including anxiety and depression are common, and may further exacerbate itch.
• What is the definition and epidemiology of chronic pruritus?
Chronic pruritus, defined as itch persisting for more than 6 weeks, is common. It may involve the entire skin (generalized pruritus) or only particular areas such as the scalp, upper back, arms, or groin (localized pruritus). Chronic pruritus increases with age, is more common in women than in men, and in Asians more than in Caucasians.
• What are the causes of chronic pruritus?
Chronic pruritus is characteristic of several dermatologic diseases (e.g., atopic eczema, psoriasis, lichen planus, and scabies) but also occurs in a variety of nondermatologic disorders. The causes of chronic pruritus can be broadly categorized into four major groups: dermatologic; systemic (e.g., cholestasis, chronic kidney disease, myeloproliferative disorders, and hyperthyroidism); neurologic (e.g., notalgia paresthetica [a distinctive itch of the upper back] and brachioradial pruritus [a characteristic itch of the arms], probably caused by spinal nerve impingement); and psychogenic. Itching of any type may elicit secondary skin changes thanks to scratching, rubbing, and picking, and thus the presence of skin findings does not rule out a systemic cause. Excoriation and nonspecific dermatitis can camouflage both cutaneous and noncutaneous causes of itch.
Morning Report Questions
Q: What is the appropriate evaluation of a patient with chronic pruritus?
A: The first step in the evaluation of chronic pruritus is to determine if the itch can be attributed to a dermatologic disease, or whether an underlying noncutaneous cause is present. A detailed review of systems and a thorough drug history should be performed. Pruritus is sometimes the first manifestation of systemic diseases such as Hodgkin’s disease or primary biliary cirrhosis, antedating other symptoms by months or longer. The skin should be examined carefully to assess for primary skin lesions. It should be recognized that excoriations, nonspecific dermatitis, prurigo nodularis, and LSC (lichen simplex chronicus) are secondary lesions, for which an underlying cause should be sought. Excessively dry skin (xerosis) usually presents with minimally detectable changes, but erythematous and scaly inflammatory patches may develop. In addition to the history and physical examination, screening studies are suggested should include a CBC (complete blood count) with differential, tests of hepatic, renal, and thyroid function, and a chest radiograph. An HIV test and sedimentation rate should also be considered.
Q: What is the role for neuroactive medications in the treatment of chronic pruritus?
A: Gabapentin and pregabalin, structural analogues of the neurotransmitter gamma-aminobutyric acid, are effective for several types of pruritus. In controlled trials in patients with CKD (chronic kidney disease) pruritus, low doses of gabapentin (100 to 300 mg three times a week) were significantly more effective in reducing itch than placebo. Case reports have described their use in practice to reduce neuropathic itch such as post herpetic itch, brachioradial pruritus, and prurigo nodularis, although there are no controlled studies of these conditions. The mechanisms of action are unclear. The most frequent adverse effects are constipation, weight gain, drowsiness, ataxia and blurred vision.