Tejesh S. Patel

The Brain Processing of Scratching

Neuroimaging studies have examined the neural networks activated by pruritus but not its behavioral response, scratching. In this study, we examine the central sensory effects of scratching using blood oxygen level-dependent functional magnetic resonance imaging (fMRI) in 13 healthy human subjects. Subjects underwent functional imaging during scratching of the right lower leg. Scratching stimulus was started 60 seconds after initiation of fMRI acquisition and was cycled between 30-second duration applications of scratching and 30-second duration applications of no stimuli. Our results show that repetitive scratching induces robust bilateral activation of the secondary somatosensory cortex, insular cortex, prefrontal cortex, inferior parietal lobe, and cerebellum. In addition, we show that the same stimulus results in robust deactivation of the anterior and posterior cingulate cortices. This study demonstrates brain areas (motor, sensory, and non-sensory) activated and deactivated by repetitive scratching. Future studies that investigate the central effects of scratching in chronic itch conditions will be of high clinical relevance.

Nocturnal itch : Why do we itch at night?

Pruritus is exacerbated at night in many systemic and dermatological diseases, resulting in reports of significantly diminished quality of life and sleep disturbances. At present, the underlying mechanisms responsible for night-time itching are not well understood. Nocturnal pruritus may be related to the circadian rhythm of itch mediators and possibly the disruption of such patterns. Diurnal changes in skin physiology, such as temperature and barrier function, may also play a role. Currently, the paucity of specific treatment options for nocturnal pruritus is alarming and needs to be addressed by future research. This review describes the scale of the problem associated with nocturnal pruritus, the impact it has on patients, possible underlying mechanisms and, lastly, treatment options.

Effect of Itch, Scratching and Mental Stress on Autonomic Nervous System Function in Atopic Dermatitis

Atopic dermatitis is a stress-responsive disorder that involves the autonomic nervous system. The current study used heart rate variability to examine the effect of itch, scratching and mental stress in atopic patients with moderate to severe disease. Twenty-one patients with active disease and 24 healthy volunteers participated in the study. Heart rate variability measurements were taken at 5 min intervals at rest and after each of 3 acute stress tests, which included histamine-induced itch at the forearm, scratching around the itch site, and the Trier Social Stress Test. Atopic patients displayed a higher heart rate than healthy controls in all 4 experimental settings, which was statistically significant using Cohens delta analysis. The very low frequency component of the power spectrum, indicative of sympathetic activity, showed a 200% increase after scratching in patients with atopic dermatitis. The high frequency component, reflecting parasympathetic tone, responded swiftly to itch and scratching in healthy controls, but displayed a limited adaptability in atopic dermatitis. This study supports the concept that atopic dermatitis is a stress-responsive disorder and involves autonomic nervous system dysfunction. Atopic subjects exhibited an overactive sympathetic response to itch and scratching, while the parasympathetic tone was persistently and rigidly elevated, showing a lack of adaptability in response to stress.

A pramoxine-based anti-itch lotion is more effective than a control lotion for the treatment of uremic pruritus in adult hemodialysis patients

Objective: The objective of this study was to evaluate the efficacy of a commercially available anti-itch lotion containing 1% pramoxine hydrochloride versus control lotion in the treatment of uremic pruritus in adult hemodialysis patients. Methods: This was a randomized, double-blind, controlled comparative trial set in a community hemodialysis center. The study population comprised 28 individuals (mean age 53.5) with moderate to severe uremic pruritus who had been receiving hemodialysis for at least 3 months. All participants were recruited from one community hemodialysis center. Topical anti-itch lotion containing 1% pramoxine was applied twice daily to all affected areas of pruritus for 4 weeks. The main outcome measure was a reduction in itch intensity. Secondary outcomes included increases in the investigators global assessment and improvement in skin hydration. Results: There was a 61% decrease in itch intensity in the treatment group, whereas a 12% reduction in itch intensity was observed in the control group. The rate of decline in itching was also greater in the treatment arm versus the control arm. No significant differences were displayed in other studied disease-related variables. Conclusion: Our study shows that individuals using pramoxine 1% lotion experienced a reduction in pruritus to a greater degree than those using the control lotion. This safe, convenient and effective topical lotion may potentially benefit the large number of patients affected by pruritus associated with end-stage renal disease.

Voxel-based morphometry and arterial spin labeling fMRI reveal neuropathic and neuroplastic features of brain processing of itch in end-stage renal disease.

Pruritus of end-stage renal disease (ESRD) is a multifactorial symptom of complex etiology not yet fully understood. In this study we have investigated the cerebral perfusion patterns at rest in ESRD patients on hemodialysis, compared with those in healthy volunteers. We have also studied the brain responses evoked by experimental itch induction in ESRD, after stimulating the two distinct histamine and cowhage itch pathways, and compared them with the responses evoked in healthy volunteers. To identify potential structural alterations in ESRD patients compared with a group of age-matched healthy volunteers, we calculated the density of gray matter for the entire brain using a voxel-based morphometric analysis. Our results indicated that gray matter density was significantly reduced in ESRD patients in the frontal, parietal, temporal, and occipital cortices, as well as in the S1, precuneus, and insula, whereas the brain stem, hippocampus, amygdala, midcingulate cortex, and nucleus accumbens displayed an increased gray matter density. Functionally, we found a significantly higher brain perfusion at baseline associated with ESRD pruritus in the anterior cingulate, insula, claustrum, hippocampus, and nucleus accumbens. The brain responses evoked by cowhage itch, which are mediated by protease-activated receptors (PAR2), displayed significant differences compared with responses in healthy individuals and were correlated with perceived itch intensity in a dual, complex manner. The inverse correlations in particular suggested that a negative feedback mechanism modulated itch intensity, when elicited in a preexistent chronic itch background.

Thermal sensory and pain thresholds in the tongue and chin change with age, but are not altered in burning mouth syndrome

Background: Burning mouth syndrome (BMS) is a chronic orofacial pain syndrome that occurs in middle‐aged and postmenopausal women and poses a therapeutic challenge to dermatologists and dentists. It has been suggested previously that BMS is a small‐fiber neuropathy.