Endocrine disorders. Approximately 4% to 11% of patients with thyrotoxicosis have pruritus.1 It has been suggested that vasodilation, increased skin temperature, and a decreased itch threshold from untreated Graves disease might be inciting factors.
Malignancy. In generalized chronic pruritus without a known cause, strongly consider the likelihood of underlying malignancy8,10; for 10% of these patients, their chronic pruritus is a paraneoplastic sign. Paraneoplastic pruritus is characterized as an itch that predates clinical onset, or occurs early in the course, of a malignancy.9 The condition is most strongly linked to cancers of the liver, gallbladder, biliary tract, hematologic system, and skin.11
Chronic pruritus affects 30% of patients with Hodgkin lymphoma.9 General pruritus can precede this diagnosis by months, even years.1 In Hodgkin lymphoma patients who are in remission, a return of pruritic symptoms can be a harbinger of recurrence.9
Neurologic causes
A recent study found that 8% to 15% of patients referred to a dermatology clinic for chronic pruritus without skin eruption had underlying neurologic pathology.12 Although the specific mechanisms of neuropathic itch are still poorly understood, it has been theorized that the itch emanates from neuronal damage, which can come from peripheral or central nervous system lesions.9
Brachioradial pruritus. There are divergent theories about the etiology of brachioradial pruritus. One hypothesis is that the condition is caused by cervical nerve-root impingement at the level of C5-C8 that leads to nerve damage2; another is that chronic exposure to sunlight causes injury to peripheral cutaneous nerves.2 Brachioradial pruritus is localized to the dorsolateral forearm; it can also involve the neck, back, shoulder, upper arm, and chest, unilaterally and bilaterally. This pruritus can be intermittent and become worse upon exposure to sunlight.2
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