![]() As the location of the underlying neural damage can be located away from the actual itchy area, scratching a neuropathic itch is rarely effective. Neuropathic itch can be caused by primary lesions or dysfunction at any point along the afferent pathway of the nervous system ( 4). Neuropathic itch results from damage to central or peripheral sensory neurons, which leads to the firing of pruritic neurons without any cutaneous pruritogenic stimuli ( 9). The mechanism or pathophysiology of psychogenic pruritus is unclear.īecause of the extensive nature of this topic, the present authors refer interested readers to the article in this issue of Dermatologic Therapy, “Neuropathic itch diagnosis and management.” The present authors limit our discussion here to the known pathophysiology of some of the more common causes of neuropathic itch. In evaluating a patient with psychogenic itch, clinicians should rule out systemic, neuropathic, and dermatologic causes of itch. Patients typically engage in self-mutilating behavior by scratching and picking their skin in an effort to remove the insect or parasite. The skin lesions seen in these patients are in response to these delusions ( 8). Delusion of parasitosis is a rare psychiatric disorder in which patients have fixed, false beliefs that their body is infested with an insect or parasite. The most well-known diagnosis with a major psychogenic itch component is delusions of parasitosis. Psychogenic itch is generally a diagnosis of exclusion and requires ruling out other causes of pruritus ( 4, 7). The incidence of patients in dermatology clinics with psychogenic itch is estimated to be 2% ( 6). Psychogenic pruritus involves brain or psychiatric abnormalities that are not yet well defined, but multiple psychiatric diagnoses including depression, obsessive compulsive disorder, anxiety, somatoform disorders, mania, psychosis, and substance abuse have been associated with itch ( 5). It typically presents with excessive impulses to scratch or pick at otherwise normal skin ( 4). ![]() ![]() Psychogenic itch is associated with psychological abnormalities and is considered psychiatric in origin. This article describes our current understanding of the pathophysiology of itch. By understanding the pathophysiology of itch, clinicians are better equipped to manage and treat patients with itch. ![]() The importance of the immune system in mediating cutaneous and neurogenic inflammation also contributes to itch but is beyond the scope of this article. This is changing as the growth of dermatologic and neuroscience-based research in the last decade has allowed for a better understanding of the neuro- and physioanatomical bases of itch. Itch has been the least understood and researched somatosensory modality. These observations have paralleled a much needed increase of investigation into the mechanisms underlying both acute and chronic itch and will ultimately lead to new and effective therapies. It is recognized that antihistamines are not effective to treat most itches. Recent studies have indicated that this frequently ignored symptom can have a major impact on health-related quality of life ( 1). Itch is the dominant symptom of a vast variety of diseases from cutaneous inflammatory conditions such as atopic dermatitis to systemic, neurologic, and autoimmune disorders such as hepatic or renal failure, multiple sclerosis, or celiac disease. ![]()
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