Functional magnetic resonance imaging in prurigo nodularis: A call to study neural sensitization phenomena

Prurigo nodularis is a chronic pruritic, inflammatory skin condition characterized by nodular skin lesions in a typical distribution pattern caused by various dermatologic and/or nondermatologic conditions. In recent years, significant advances have been made in the understanding of the cutaneous pathophysiology of prurigo nodularis, resulting in novel treatment options such as interleukin-4, -13, -17, and -31 or Janus kinase inhibitors. Many aspects of the neurophysiology are largely unknown, including the processing in the central structural and functional network involved in prurigo nodularis. Functional neuroimaging allows noninvasive assessment of brain function and structure. Due to its high spatial resolution and temporal precision, functional magnetic resonance imaging has proven to be a suitable method for exploring neural mechanisms and assessing pharmacologic effects in dermatologic research. In this systematic review, the current knowledge of functional magnetic resonance imaging in the context of prurigo nodularis and its centrally active treatment options is summarized.

Neuroimaging Characteristics of Pruritus Induced by Eczema: An fMRI Study

OBJECTIVE

To explore the neuroimaging characteristics of eczema-induced pruritus with resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

A total of 42 patients with eczema were recruited in the PE group, and 42 healthy participants were included in the HC group. The Visual Analogue Score (VAS), 12-Item Pruritus Severity Scale (12-PSS), Pittsburgh Sleep Quality Index (PSQI), and Self-Rating Anxiety Scale (SAS) were recorded in the PE group. The different values of fraction amplitude of low-frequency fluctuation (fALFF) and functional connectivity (FC) were compared after rs-fMRI scanning.

RESULTS

Compared with the HC group, the fALFF values of the left precentral gyrus, left postcentral gyrus, left supplementary motor area (SMA), and left midcingulate cortex in the PE group were increased. The FC values between the left precentral gyrus, bilateral superior temporal gyrus, bilateral hippocampus, and left inferior occipital gyrus in the PE group were decreased. The FC values between left SMA and bilateral superior temporal gyrus in the PE group were decreased. The 12-PSS score was positively correlated with fALFF value of the left precentral gyrus and left postcentral gyrus.

CONCLUSION

Pruritus caused increased spontaneous activity in given cerebral regions, involving the perception of itch, control of scratching movements, and expression of itch-related emotions. Meanwhile, there is a correlation between fALFF values of given cerebral regions and clinical scales, which provided potential neurobiological markers for the future study of pruritus.

A Narrative Review on Stress and Itch: What We Know and What We Would Like to Know

Itch is one of the most prevalent symptoms experienced by patients with inflammatory skin conditions, yet it is also one of the most debilitating. Patients suffering from chronic itch have been found to have significantly higher stress levels compared with those not experiencing itch. In fact, recent studies have revealed a bidirectional relationship between stress and itch, where each condition worsens the other. This is thought to be driven by the vicious itch-scratch cycle, which is fueled by underlying inflammation. The precise molecular pathways and mediators involved, however, remain unclear. This narrative review discusses the existing research on the relationship between stress and itch and outlines future research directions that will be necessary to advance our understanding and treatment of these conditions. Given that the effective management of both symptoms often requires a combined treatment approach, further investigation into their shared mechanisms is essential for identifying successful therapies and improving patient outcomes.

The neuroscience of itch in relation to transdiagnostic psychological approaches

The experience of itch and its associated chronic conditions (i.e., atopic dermatitis) form a significant burden of disease. Knowledge of how the brain processes itch, that might occur uniquely for chronic itch populations, could be used to guide more effective psychotherapeutic interventions for these groups. To build the evidence base for such approaches, we conducted a series of coordinates-based fMRI analyses, to identify the shared neural mechanisms for itch across the published literature. Upon so doing, we identified a core "itch network" that spans the Basal Ganglia/Thalamus, Claustrum and Insula. Additionally, we found evidence that the Paracentral Lobule and Medial Frontal Gyrus, regions associated with cognitive control and response inhibition, deactivate during itch. Interestingly, a separate analysis for chronic itch populations identified significant recruitment of the Left Paracentral Lobule, potentially suggesting the recruitment of cognitive control mechanisms to resist the urge to scratch. We position these results in light of further integrative studies that could use neuroimaging alongside clinical studies, to explore how transdiagnostic psychological approaches-such as mindfulness and compassion training-might help to improve quality of life for individuals who experience chronic itch.

Efficacy of a Nursing Skin Care Protocol in the Prevention of Skin-Related Problems Among Newly Diagnosed Diabetic Patients: A Pilot Study

Introduction Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels, affecting millions worldwide. Among the various complications associated with diabetes, skin-related problems represent a significant concern, particularly for newly diagnosed patients. Altered blood circulation, compromised immune responses and nerve damage increase the risk of skin issues in this vulnerable population. Effective nursing interventions are crucial in managing and preventing diabetes-related skin problems. A nursing skin care protocol tailored to the unique needs of newly diagnosed diabetic patients has the potential to reduce the incidence and severity of skin complications, leading to improved patient outcomes and enhanced quality of life. This study aims to assess the efficacy of a nursing skin care protocol in preventing skin-related problems among newly diagnosed diabetic patients. By analyzing the impact of the protocol on patient outcomes and exploring the significance of early intervention and patient education, this research seeks to provide valuable insights into the importance of proactive skin care management in diabetes care. Methods A randomized controlled trial was conducted at Acharya Vinoba Bhave Rural Hospital in India to evaluate the efficacy of a nursing skin care protocol in preventing skin problems among newly diagnosed diabetic patients. The study included 30 patients who met specific inclusion criteria and excluded those with critical illness or undergoing skin treatment. Data was collected using a questionnaire and standardized tools. Statistical analysis demonstrated the protocol's effectiveness in reducing skin-related issues. The results highlight the importance of early intervention and personalized nursing care in diabetic management, promoting better patient outcomes and overall well-being. Results The results of the study demonstrate the efficacy of the nursing skin care protocol in reducing pruritus and dry skin problems among newly diagnosed diabetic patients. The experimental group showed a substantial improvement, with higher efficacy gains for both pruritus (66.70%) and dry skin (86.70%) compared to the control group (pruritus: 26.70%, dry skin: 33.30%). These findings highlight the potential benefits of implementing the nursing skin care protocol to alleviate skin-related issues in this patient population. The study supports the importance of early intervention and tailored nursing care in managing diabetic skin problems, which could improve patient outcomes and overall well-being. Conclusion In conclusion, the nursing skin care protocol effectively prevented and reduced skin-related problems among newly diagnosed diabetic patients. The experimental group showed significant improvements in pruritus and dry skin compared to the control group. Early intervention and personalized nursing care are crucial in managing diabetic skin issues and enhancing patient well-being. Implementing the nursing skin care protocol can lead to a better quality of life for diabetic patients by addressing skin concerns. Further research and application of this protocol hold promise for managing skin-related complications in diabetes effectively.

Altered resting-state functional connectivity of default mode network in brachioradial pruritus

BACKGROUND

Patients with chronic pruritus (CP) have a low quality of life, thus it is important to gain a better understanding of the underlying processes. Previous functional magnetic resonance imaging studies at rest (rs-fMRI) have shown that mainly areas associated with the default mode network (DMN), sensorimotor (SMN), frontoparietal (FPN) and salience networks (SN) are involved in the processing of itch in patients with chronic pruritus (CP), as well as the cortico-striatal circuit, which is involved in the motoric preparation of scratching. rs-fMRI studies on functional connectivity (FC) patterns of resting-state networks (RSNs) in patients with inflammatory atopic dermatitis (AD) or with neuropathic brachioradial pruritus (BRP) compared to healthy controls (HC) are lacking.

OBJECTIVES

The main goals of this study were to investigate whether functional connectivity within networks and areas associated with itch detection and processing are altered in patients with AD and BRP compared to matched healthy controls by rsfMRI, respectively.

METHODS

Patients with AD (n = 28) and with BRP (n = 28) were compared to corresponding matched healthy controls by rsfMRI. Group specific RSNs were identified by independent component analysis (ICA) and between-group differences in the RSNs were analyzed by dual regression technique. Seed-based functional connectivity was analyzed in several itch-related brain regions belonging to the DMN, SN and FPN, respectively.

RESULTS

ICA and seed-based analyses revealed decreased functional connectivity in BRP compared to HC specially within the DMN including the precuneus and cingulate cortex. For AD patients in comparison to HC, as well as when BRP and AD patients when compared directly, no significant FC differences at rest were seen.

CONCLUSIONS

Our findings point towards decreased FC particularly in the DMN at rest in patients with BRP. These results seem to indicate that central connectivity patterns at rest differentially encode itch in BRP and AD.

The Trinity of Skin: Skin Homeostasis as a Neuro-Endocrine-Immune Organ

For a long time, skin was thought to be no more than the barrier of our body. However, in the last few decades, studies into the idea of skin as an independent functional organ have gradually deepened our understanding of skin and its functions. In this review, we gathered evidence that presented skin as a "trinity" of neuro-endocrine-immune function. From a neuro perspective, skin communicates through nerves and receptors, releasing neurotrophins and neuropeptides; from an endocrine perspective, skin is able to receive and secrete most hormones and has the cutaneous equivalent of the hypothalamic-pituitary-adrenal (HPA) axis; from an immune perspective, skin is protected not only by its physical barrier, but also immune cells and molecules, which can also cause inflammation. Together as an organ, skin works bidirectionally by operating peripheral neuro-endocrine-immune function and being regulated by the central nervous system, endocrine system and immune system at the same time, maintaining homeostasis. Additionally, to further explain the "trinity" of cutaneous neuro-endocrine-immune function and how it works in disease pathophysiology, a disease model of rosacea is presented.

Functional Magnetic Resonance Imaging and Applications in Dermatology

As a noninvasive imaging modality able to show the dynamic changes in neurologic activity, functional magnetic resonance imaging has revolutionized the ability to both map and further understand the functional regions of the brain. Current applications range from neurosurgical planning to an enormous variety of investigational applications across many diverse specialties. The main purpose of this article is to provide a foundational understanding of how functional magnetic resonance imaging is being used in research by outlining the underlying basic science, specific methods, and direct investigational and clinical applications. In addition, the use of functional magnetic resonance imaging in current dermatological research, especially in relation to studies concerning the skin‒brain axis, is explicitly addressed. This article also touches on the advantages and limitations concerning functional magnetic resonance imaging in comparison with other similar techniques.

Itch: Pathogenesis and treatment

Itch pathogenesis is broadly characterized into histaminergic and nonhistaminergic pathways and transmitted via 2 main receptor families: G protein-coupled receptors and transient receptor potential channels. In the skin, itch is primarily transmitted by unmyelinated type C and thinly myelinated type Aδ nerve fibers. Crosstalk between the immune and neural systems modulates itch transmission at the skin, spinal cord, and brain. Among the many known pruritogens, Th2 cytokines, such as interleukin-4, interleukin-13, interleukin-31, and thymic stromal lymphopoietin, are particularly important mediators that signal through shared Janus kinase pathways, representing novel targets for novel itch therapeutics. Emerging evidence has also revealed that the opioidergic system is a potent modulator of itch transmission, with increased μ-opioid activity and decreased κ-opioid activity contributing to itch pathogenesis. Optimal management of itch requires that treatment approaches be tailored to specific etiologic itch subtypes. When the etiology is unknown and patients are given a diagnosis of chronic pruritus of unknown origin, treatment should be guided by the presence of Th2 polarization, often reflected by increased blood eosinophils. In the second article of this 2-part series, we outline our current understanding of itch pathogenesis and discuss available and emerging treatments for itch.

Chronic Kidney Disease-Associated Itch (CKD-aI) in Children-A Narrative Review

Chronic kidney disease (CKD) is a condition of widespread epidemiology and serious consequences affecting all organs of the organism and associated with significant mortality. The knowledge on CKD is rapidly evolving, especially concerning adults. Recently, more data is also appearing regarding CKD in children. Chronic itch (CI) is a common symptom appearing due to various underlying dermatological and systemic conditions. CI may also appear in association with CKD and is termed chronic kidney disease-associated itch (CKD-aI). CKD-aI is relatively well-described in the literature concerning adults, yet it also affects children. Unfortunately, the data on paediatric CKD-aI is particularly scarce. This narrative review aims to describe various aspects of CKD-aI with an emphasis on children, based on the available data in this population and the data extrapolated from adults. Its pathogenesis is described in details, focusing on the growing role of uraemic toxins (UTs), as well as immune dysfunction, altered opioid transmission, infectious agents, xerosis, neuropathy and dialysis-associated aspects. Moreover, epidemiological and clinical aspects are reviewed based on the few data on CKD-aI in children, whereas treatment recommendations are proposed as well, based on the literature on CKD-aI in adults and own experience in managing CI in children.

Itch processing in the brain

Itch is a sensation defined as the urge to scratch. The central mechanisms of itch are being increasingly studied. These studies are usually based on experimental itch induction methods, which can be classified into the following categories: histamine-induced, induction by other non-histamine chemicals (e.g. cowhage), physically induced (e.g. electrical) and mentally induced (e.g. audio-visual). Because pain has been more extensively studied, some extrapolations to itch can be proposed and verified by experiments. Recent studies suggest that the itch-processing network in the brain could be disrupted in certain diseases. This disruption could be related to the implication of new regions or the exclusion of already engaged brain regions from itch-processing network in the brain.

Itching as the onset of pain (part 2)

Itching of the skin is a particularly unpleasant subjective sensation that causes the need to scratch. Physiological itching occurs in response to environmental irritants (friction, insect crawling, temperature changes, etc.) and disappears after elimination of the cause. Pathological itching is caused by changes in the skin or throughout the body and causes a strong need to get rid of itching by combing or any other method. Itching is a common symptom of local (dermatological) or general (systemic) disease. It can be limited (localized) or diffuse (generalized).One of the causes of itching is often noted endocrine diseases and metabolic disorders: hyper- and hypofunction of the thyroid gland, diabetes mellitus and hyperparathyroidism. In thyroid hyperfunction, generalized (inconstant and little-pronounced) itching of the skin is observed in the clinical picture only in 10 % of patients. It is accepted that itching of the skin in thyrotoxicosis syndrome is due to increased activity of kinin in combination with an increase in major metabolism and an increase in body and skin temperature (123).Itching caused by impaired bile secretion is characteristic of many diseases of the liver: primary biliary cirrhosis, sclerosing cholangitis, viral hepatitis caused by cholestasis medications and other causes of obstructive jaundice. It is in these cases that prurigo is usually generalized, but in some typical cases it is more pronounced on the feet and palms. With this pathology, itching is caused by obstruction of the biliary tract, however, and to this day, no close correlation has been found between serum bilirubin and the severity of itching.If it was previously thought that itching in pathology of the peripheral or central nervous system, such as multiple sclerosis, neuropathy, compression or irritation of nerves (e.g., paraesthetic dorsalgia, brachioradial itching) is also a significant symptom, then modern studies prove that in more cases, itching is not characteristic of most pathologies of the nervous system, so after a detailed anamnesis, examination and initial research, the patient should be referred to a related specialist, except in cases of about obvious postherpetic neuropathy, painless paresthesia, or brachioradial itching, which can often be guided in the provision of primary care.Instead, there are some psychological conditions and a number of psychiatric illnesses (obsessive-compulsive disorders, depression, and parasite illusions) that are most commonly diagnosed with the exclusion method. Neurotic squabbles are scattered on the body of the excorii, covered with scales that may occur in any area of the body that the patient may reach, but are often limited by limbs.

Effects of Stress on Itch

PURPOSE

Psychological stress and ensuing modulation of the immune and nervous systems can have a significant impact on itch. Stress can exacerbate itch and vice versa, resulting in a vicious cycle that can greatly impair a patient's quality of life. This review summarizes the association between stress and itch, elucidates the mechanism by which these two phenomena influence one another, and explores treatment modalities that aim to reduce stress-induced itch.

METHODS

A complete search of the PubMed and Google Scholar databases was completed and literature pertinent to this review was compiled.

FINDINGS

Both acute and chronic stress can significantly affect itch in healthy individuals and in those diagnosed with itchy skin diseases as well as systemic diseases, thus resulting in a vicious cycle in which stress exacerbates itch and vice versa. The mechanisms by which stress induces or aggravates itch include both central and peripheral activation of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system. Activation of these systems, in turn, affects the mast cells, keratinocytes, and nerves that secrete neuropeptides, such as substance P, nerve growth factor, acetylcholine, histamine, and itchy cytokines. A dysfunctional parasympathetic response is thought to be involved in the chronic stress/itch response. Brain structures associated with emotion, such as the limbic system and periaqueductal gray, which work on the descending facilitation of itch, play a significant role in stress-induced itch.

IMPLICATIONS

As specific brain structures are associated with stress, drug treatments targeting these areas (ie, γ-aminobutyric acid-ergic drugs, serotonin and norepinephrine reuptake inhibitors) may help to modulate itch. Stress can also be combatted using nonpharmacologic treatments such as cognitive-behavioral therapies and stress-relieving holistic approaches (eg, yoga, acupuncture).

What is new in the psychology of chronic itch?

Itch is often regarded as unpleasant or bothersome and is accompanied by symptoms of distress and impairments in daily life. The biopsychosocial model of chronic itch describes how psychological factors can contribute to the improvement or exacerbation of chronic itch and related scratching behaviour. Recent research underlines the important role of cognitive-affective information processing, such as attention, affect and expectancies. This may not only play a role for acute itch states, but may particularly apply to the process of itch chronification, for example, due to the vicious cycle in which these factors shape the experience of itch. The present paper focuses on new insights into the relation between itch and the cognitive-affective factors of attention, affect and expectancies. These factors are thought to play a possible aggravating role in itch in the long term and have received increasing attention in the recent empirical literature on maintaining and exacerbating factors for chronic physical symptoms. Possible psychophysiological and neurobiological pathways regarding these factors are discussed, as well as possible intervention methods.

Can we use psychoactive drugs to treat pruritus?

Pruritus is a frequent complaint both in dermatology and general medicine. This burdensome symptom has a complex and multifactorial pathogenesis, with the key involvement of central nervous system in its development. Psychoactive drugs (psychopharmaceuticals) encompass several therapeutic groups utilized mainly in psychiatry. However, these drugs are occasionally used in dermatological practice and may contribute to alleviation of pruritus in a variety of cutaneous and extracutaneous disorders. This review article summarizes the role of H1-antihistamines, antidepressants, antipsychotics and antiepileptics in managing pruritus.

Why does stress aggravate itch? A possible role of the amygdala

Stress is the exacerbating factor of itch across patients with chronic itch due to different origins. However, the precise mechanisms behind stress-induced exacerbation of itch remain unknown. Chronic stress induces hyperexcitability of the amygdala, the centre of emotional processing. Recent findings on the itch neuronal pathways support a pivotal role of the amygdala for itch processing. We hypothesized that itch is enhanced by stress through hyperexcitation of the amygdala. Modulation of amygdala activity, therefore, may have therapeutic potential in the treatment of chronic itch.

Relations between a standardized experimental stressor and cutaneous sensory function in patients with chronic pruritus and healthy controls: an experimental case-control study

Background

While chronic pruritus (CP) is a frequent symptom, many aspects of its underlying pathophysiological mechanisms still need elucidation. Research on sensory cutaneous function and on the influence of stress has been conducted mainly in patients with atopic dermatitis but is lacking for patients with CP.

Objective

To assess whether a standardized social stressor influences cutaneous sensory function in patients with CP in comparison with healthy controls (HC).

Methods

Case–control study; 33 CP and 30 HC were submitted to the standardized quantitative sensory testing protocol before and after the Trier Social Stress Test and 1 h later. Intraepidermal nerve fibre density (IENFD) was determined.

Results

Mechanical pain sensitivity and mechanical detection thresholds were significantly higher in CP than in HC, and mechanical detection thresholds increased more in CP than in HC over the three measurements. In both groups, cold pain threshold increased and heat pain threshold decreased from before to after the stress test and remained constant 1 h later. Only in CP, almost all QST tests induced at least a small amount of pruritus, which was not significantly altered by the stress test. IENFD in pruritic skin was significantly reduced in CP when compared to healthy controls.

Conclusion

Peripheral thermal sensory function was not altered in CP despite reduced IENFD in lesional skin, but we could demonstrate central sensitization processes specifically in CP and influences of an acute stressor inducing more sensitivity to thermal pain in both groups.

Itch and psyche: psychiatric aspects of pruritus

Itch, also referred to as pruritus, is an unpleasant cutaneous sensation provoking the desire to scratch. It is often an uncomfortable, subjective sensation responsible for decreased quality of life in a variety of psychodermatological conditions. Comorbid psychiatric conditions, including depression and anxiety, are frequently associated with itch and scratch cycle. The reciprocal and intricate relationship between the psyche and itch has been widely studied. The neurobiology of itch involves the complexity of specific mediators, itch-related neuronal pathways, and central processing of itch. The connection between itch and the psyche can be grouped under three headings: pruritic diseases with psychosocial sequelae, pruritic diseases aggravated by psychosocial factors, and psychiatric disorders causing pruritus. Itch and pain modulation go together in most circumstances and involve various substances including histamine, interleukins, protease-activated receptors, transient receptor potential receptors, opioids, and cannabinoids. The close interaction between keratinocytes and nerve endings modulating pain and itch also play a major role. Management of itch associated with its psychosomatic components is directed at an underlying cause and adopting a holistic approach to address not only dermatologic and somatosensory aspects, but also the cognitive, emotional, and psychosocial components. An integrated multidisciplinary team consisting of a dermatologist, psychiatrist, psychologist, and social worker is vital in addressing the multifaceted aspects of pruritus.

The vicious cycle of itch and anxiety

Chronic itch is associated with increased stress, anxiety, and other mood disorders. In turn, stress and anxiety exacerbate itch, leading to a vicious cycle that affects patient behavior (scratching) and worsens disease prognosis and quality of life. This cycle persists across chronic itch conditions of different etiologies and even to some extent in healthy individuals, suggesting that the final common pathway for itch processing (the central nervous system) plays a major role in the relationship between itch and anxiety. Pharmacological and nonpharmacological treatments that reduce anxiety have shown promising anti-itch effects. Further research is needed to establish specific central mechanisms of the itch-anxiety cycle and provide new targets for treatment.

The functional and structural alterations of the striatum in chronic spontaneous urticaria

The brain has long been known to be the regulation center of itch, but the neuropathology of chronic itch, such as chronic spontaneous urticaria (CSU), remains unclear. Thus, we aimed to explore the brain areas involved in the pathophysiology of CSU in hopes that our results may provide valuable insights into the treatment of chronic itch conditions. 40 CSU patients and 40 healthy controls (HCs) were recruited. Urticaria activity scores 7 (UAS7) were collected to evaluate patient’s clinical symptoms. Amplitude of low frequency fluctuations (ALFF), voxel-based morphometry (VBM), and seed-based resting-state functional connectivity (rs-FC) analysis were used to assess brain activity and related plasticity. Compared with HCs, CSU patients exhibited 1) higher ALFF values in the right ventral striatum / putamen, which were positively associated with clinical symptoms as measured by UAS7; 2) gray matter volume (GMV) increase in the right ventral striatum and putamen; and 3) decreased rs-FC between the right ventral striatum and the right occipital cortex and between the right putamen and the left precentral gyrus. Using multiple-modality brain imaging tools, we demonstrated the dysfunction of the striatum in CSU. Our results may provide valuable insights into the neuropathology and development of chronic itch.