In vivo imaging of patients with chronic pruritus of unknown origin reveals partial sweat duct obstruction with partial itch resolution upon retinoid treatment

BackgroundChronic pruritus of unknown origin (CPUO) is poorly understood and lacks effective treatment options.ObjectivesWe aimed to elucidate abnormalities in the sweat apparatus of patients with CPUO, and to assess efficacy and safety of treatment with systemic retinoids.MethodsAn initial case–control study included 20 affected patients and five healthy controls, for whom heat and sweating were induced, either through a standardized exercise protocol or ingestion of hot water. In vivo high-definition optical coherence tomography, whole-body starch-iodine testing, and skin biopsy for immunofluorescence staining were done to evaluate for sweat duct obstruction. A subsequent retrospective cohort analysis included 56 patients with CPUO, seen at an Itch subspecialty clinic of a single tertiary referral centre, who failed conventional treatments and were treated with isotretinoin and/or acitretin from May 2014 to November 2020. Treatment response to retinoids was defined as a sustained reduction in itch score of ≥2/10. Safety was assessed by proportion stopping treatment due to side effects.ResultsIn vivo imaging in 19 (95%) patients revealed features of partial keratinaceous sweat duct obstruction with statistically significant luminal dilatation compared to controls. Immunofluorescence studies of three patients’ paired lesional/non-lesional biopsies revealed dermcidin accumulation within sweat glands coupled with dermcidin leakage in itchy skin. Fifty-six patients (mean [SD] age 55.2 [17.5] years, 69.6% male) were treated with systemic retinoids. Mean (SD) duration of itch was 116.3 (140.4) months and mean (SD) itch score was 8.2 (1.8). Forty-one (73.2%) initially received isotretinoin, and 15 (26.8%) acitretin. At three months, mean itch score reduced by 2.38 (95% CI -3.2 to −1.6, p < 0.0001). Thirty-eight (67.9%) had a sustained response. Eight (14.81%) achieved an itch score of 0 or 1, with four stopping treatment for a mean (SD) of 318.5 (291.2) days without relapse. Eight (14.3%) stopped or switched retinoid due to adverse effects, with similar incidences between both retinoids, the commonest being dryness.ConclusionBased on novel findings from physiological imaging studies identifying partial keratinaceous sweat duct obstruction in CPUO, we instituted systemic retinoid treatment to address the underlying pathology. In patients who failed conventional therapies, the treatment appears effective and safe

Cowhage-Induced Itch as an Experimental Model for Pruritus. A Comparative Study with Histamine-Induced Itch

Histamine is the prototypical pruritogen used in experimental itch induction. However, in most chronic pruritic diseases, itch is not predominantly mediated by histamine. Cowhage-induced itch, on the other hand, seems more characteristic of itch occurring in chronic pruritic diseases.We tested the validity of cowhage as an itch-inducing agent by contrasting it with the classical itch inducer, histamine, in healthy subjects and atopic dermatitis (AD) patients. We also investigated whether there was a cumulative effect when both agents were combined.Fifteen healthy individuals and fifteen AD patients were recruited. Experimental itch induction was performed in eczema-free areas on the volar aspects of the forearm, using different itch inducers: histamine, cowhage and their combination thereof. Itch intensity was assessed continuously for 5.5 minutes after stimulus application using a computer-assisted visual analogue scale (COVAS).In both healthy and AD subjects, the mean and peak intensity of itch were higher after the application of cowhage compared to histamine, and were higher after the combined application of cowhage and histamine, compared to histamine alone (p<0.0001 in all cases). Itch intensity ratings were not significantly different between healthy and AD subjects for the same itch inducer used; however AD subjects exhibited a prolonged itch response in comparison to healthy subjects (p<0.001).Cowhage induced a more intense itch sensation compared to histamine. Cowhage was the dominant factor in itch perception when both pathways were stimulated in the same time. Cowhage-induced itch is a suitable model for the study of itch in AD and other chronic pruritic diseases, and it can serve as a new model for testing antipruritic drugs in humans

Itch in ethnic populations

Racial and ethnic differences in the prevalence and clinical characteristics of itch have rarely been studied. The aim of this review is to highlight possible associations between ethnicity and different forms of chronic itch. We provide a current review of the prevalence of different types of itch in ethnic populations. Genetic variation may significantly affect receptors for itch as well as response to anti-pruritic therapies. Primary cutaneous amyloidosis, a type of pruritic dermatosis, is particularly common in Asians and rare in Caucasians and African Americans, and this may relate to a genetic polymorphism in the Interleukin-31 receptor. Pruritus secondary to the use of chloroquine for malaria is a common problem for African patients, but is not commonly reported in other ethnic groups. In patients with primary biliary cirrhosis, pruritus is more common and more severe in African Americans and Hispanics compared with Caucasians. Racial and ethnic differences in itch and its medical care are poorly understood. Research is needed to examine biological, psychosocial, and lifestyle factors that may contribute to these disparities

Bullous eosinophilic annular erythema

Eosinophilic annular erythema is an idiopathic acute eosinophilic dermatosis. It is a rare condition, with approximately 30 cases reported in the English literature. It features annular, figurate urticarial edematous plaques primarily affecting the trunk and proximal limbs. During evaluation of a patient, secondary causes of eosinophilic inflammation such as allergy-related conditions (eczema, drug, urticaria, contact dermatitis), parasitic infestations, and autoimmune dermatoses will need to be excluded. We present an unusual case of a 47-year-old patient who developed this condition

Bullous eosinophilic annular erythema

Eosinophilic annular erythema is an idiopathic acute eosinophilic dermatosis. It is a rare condition, with approximately 30 cases reported in the English literature. It features annular, figurate urticarial edematous plaques primarily affecting the trunk and proximal limbs. During evaluation of a patient, secondary causes of eosinophilic inflammation such as allergy-related conditions (eczema, drug, urticaria, contact dermatitis), parasitic infestations, and autoimmune dermatoses will need to be excluded. We present an unusual case of a 47-year-old patient who developed this condition

Psychosomatic factors in pruritus

Pruritus and psyche are intricately and reciprocally related, with psychophysiological evidence and psychopathological explanations helping us to understand their complex association. Their interaction may be conceptualized and classified into 3 groups: pruritic diseases with psychiatric sequelae, pruritic diseases aggravated by psychosocial factors, and psychiatric disorders causing pruritus. Management of chronic pruritus is directed at treating the underlying causes and adopting a multidisciplinary approach to address the dermatologic, somatosensory, cognitive, and emotional aspects. Pharmcotherapeutic agents that are useful for chronic pruritus with comorbid depression and/or anxiety comprise selective serotonin reuptake inhibitors, mirtazapine, tricyclic antidepressants (amitriptyline and doxepin), and anticonvulsants (gabapentin, pregabalin); the role of neurokinin receptor-1 antagonists awaits verification. Antipsychotics are required for treating itch and formication associated with schizophrenia and delusion of parasitosis (including Morgellons disease). (c) 2013 Elsevier Inc. All rights reserved