Altered manifestations of skin disease at sites affected by neurological deficit

Sensory neurons: An integrated component of innate immunity

The sensory nervous system possesses the ability to integrate exogenous threats and endogenous signals to mediate downstream effector functions. Sensory neurons have been shown to activate or suppress host defense and immunity against pathogens, depending on the tissue and disease state. Through this lens, pro- and anti-inflammatory neuroimmune effector functions can be interpreted as evolutionary adaptations by host or pathogen. Here, we discuss recent and impactful examples of neuroimmune circuitry that regulate tissue homeostasis, autoinflammation, and host defense. Apparently paradoxical or conflicting reports in the literature also highlight the complexity of neuroimmune interactions that may depend on tissue- and microbe-specific cues. These findings expand our understanding of the nuanced mechanisms and the greater context of sensory neurons in innate immunity.

Peripheral nerve repair is associated with augmented cross-tissue inflammation following vascularized composite allotransplantation

Introduction

Vascularized composite allotransplantation (VCA), with nerve repair/coaptation (NR) and tacrolimus (TAC) immunosuppressive therapy, is used to repair devastating traumatic injuries but is often complicated by inflammation spanning multiple tissues. We identified the parallel upregulation of transcriptional pathways involving chemokine signaling, T-cell receptor signaling, Th17, Th1, and Th2 pathways in skin and nerve tissue in complete VCA rejection compared to baseline in 7 human hand transplants and defined increasing complexity of protein-level dynamic networks involving chemokine, Th1, and Th17 pathways as a function of rejection severity in 5 of these patients. We next hypothesized that neural mechanisms may regulate the complex spatiotemporal evolution of rejection-associated inflammation post-VCA.

Methods

For mechanistic and ethical reasons, protein-level inflammatory mediators in tissues from Lewis rats (8 per group) receiving either syngeneic (Lewis) or allogeneic (Brown-Norway) orthotopic hind limb transplants in combination with TAC, with and without sciatic NR, were compared to human hand transplant samples using computational methods.

Results

In cross-correlation analyses of these mediators, VCA tissues from human hand transplants (which included NR) were most similar to those from rats undergoing VCA + NR. Based on dynamic hypergraph analyses, NR following either syngeneic or allogeneic transplantation in rats was associated with greater trans-compartmental localization of early inflammatory mediators vs. no-NR, and impaired downregulation of mediators including IL-17A at later times.

Discussion

Thus, NR, while considered necessary for restoring graft function, may also result in dysregulated and mis-compartmentalized inflammation post-VCA and therefore necessitate mitigation strategies. Our novel computational pipeline may also yield translational, spatiotemporal insights in other contexts.

Clinical Course of Atopic Dermatitis in an Adult with Amyotrophic Lateral Sclerosis: Aetiological Implications of Voluntary Movements and Dermatitis Severity

Abstract is missing (Short communication)

Cutaneous Neuroimmune Interactions in Peripheral Neuropathic Pain States

Bidirectional interplay between the peripheral immune and nervous systems plays a crucial role in maintaining homeostasis and responding to noxious stimuli. This crosstalk is facilitated by a variety of cytokines, inflammatory mediators and neuropeptides. Dysregulation of this delicate physiological balance is implicated in the pathological mechanisms of various skin disorders and peripheral neuropathies. The skin is a highly complex biological structure within which peripheral sensory nerve terminals and immune cells colocalise. Herein, we provide an overview of the sensory innervation of the skin and immune cells resident to the skin. We discuss modulation of cutaneous immune response by sensory neurons and their mediators (e.g., nociceptor-derived neuropeptides), and sensory neuron regulation by cutaneous immune cells (e.g., nociceptor sensitization by immune-derived mediators). In particular, we discuss recent findings concerning neuroimmune communication in skin infections, psoriasis, allergic contact dermatitis and atopic dermatitis. We then summarize evidence of neuroimmune mechanisms in the skin in the context of peripheral neuropathic pain states, including chemotherapy-induced peripheral neuropathy, diabetic polyneuropathy, post-herpetic neuralgia, HIV-induced neuropathy, as well as entrapment and traumatic neuropathies. Finally, we highlight the future promise of emerging therapies associated with skin neuroimmune crosstalk in neuropathic pain.

Role of neuroimmune circuits and pruritus in psoriasis

Psoriasis is a chronic inflammatory skin disease presenting with an array of clinical phenotypes, often associated with pruritus. Environmental and psychological stressors can exacerbate psoriasis symptoms and provoke flares. Recent studies suggest a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis in some patients with psoriasis that can result in immune dysregulation. The immune system, in turn, can communicate with the nervous system to induce, maintain or aggravate psoriasis. In the skin, peripheral sensory as well as autonomic nerves control release of inflammatory mediators from dendritic cells, mast cells, T cells or keratinocytes, thereby modulating inflammatory responses and, in case of sensory nerves, pruritus. In response to the environment or stress, cytokines, chemokines, proteases, and neuropeptides fluctuate in psoriasis and influence immune responses as well as nerve activity. Furthermore, immune cells communicate with sensory nerves which control release of cytokines, such as IL-23, that are ultimately involved in psoriasis pathogenesis. Nerves also communicate with keratinocytes to induce epidermal proliferation. Notably, in contrast to recent years the debilitating problem of pruritus in psoriasis has been increasingly appreciated. Thus, investigating neuroimmune communication in psoriasis will not only expand our knowledge about the impact of sensory nerves in inflammation and pruritus and give new insights into the impact of environmental factors activating neuroimmune circuits or of stress in psoriasis, but may also lead to novel therapies. This review summarizes the relevant literature on the role of neuroimmune circuits, stress and how the central HPA axis and its peripheral equivalent in the skin, impact psoriasis.

The Neuroimmune Axis in Skin Sensation, Inflammation, and Immunity

Although connections between the immune and nervous systems have long been recognized, the precise mechanisms that underlie this relationship are just starting to be elucidated. Advances in sensory biology have unveiled novel mechanisms by which inflammatory cytokines promote itch and pain sensations to coordinate host-protective behavioral responses. Conversely, new evidence has emphasized the importance of immune cell regulation by sensory neurons. By focusing on itch biology and how it has been informed by the more established field of pain research, we highlight recent interdisciplinary studies that demonstrate how novel neuroimmune interactions underlie a diversity of sensory, inflammatory, and infectious diseases.

Physiology and Pathophysiology of Itch

Itch is a topic to which everyone can relate. The physiological roles of itch are increasingly understood and appreciated. The pathophysiological consequences of itch impact quality of life as much as pain. These dynamics have led to increasingly deep dives into the mechanisms that underlie and contribute to the sensation of itch. When the prior review on the physiology of itching was published in this journal in 1941, itch was a black box of interest to a small number of neuroscientists and dermatologists. Itch is now appreciated as a complex and colorful Rubik's cube. Acute and chronic itch are being carefully scratched apart and reassembled by puzzle solvers across the biomedical spectrum. New mediators are being identified. Mechanisms blur boundaries of the circuitry that blend neuroscience and immunology. Measures involve psychophysics and behavioral psychology. The efforts associated with these approaches are positively impacting the care of itchy patients. There is now the potential to markedly alleviate chronic itch, a condition that does not end life, but often ruins it. We review the itch field and provide a current understanding of the pathophysiology of itch. Itch is a disease, not only a symptom of disease.

[Two cases of unilateral chilblains associated with monoparesis]

BACKGROUND

Chilblains are inflammatory dermal lesions associated with hypersensitivity to cold, and they occur on the extremities bilaterally and symmetrically. Their onset during the course of pro-thermogenic and autoimmune diseases has been widely reported, but the association with predisposing locoregional causes is not well known.

PATIENTS AND METHODS

Case 1: a 57-year-old man, who smoked 80 packets per year, presenting a deficit of the levator muscles in his right foot following lumbar sciatica with paralysis of L5, consulted for unilateral necrotic lesions of the toes recurring each winter in the paralysed limb only. Case 2: a 60-year-old man had a previous history of liposarcoma of the right side treated with radiotherapy and surgery, resulting in sequelae of monoparesis and radiation-induced arteritis. Each winter, he presented recurring unilateral purpuric macules of the toes on his right foot, with no necrotic progression. In both cases, clinical examination, disease progression over time, histology and laboratory tests confirmed the diagnosis of idiopathic chilblains.

CONCLUSION

The physiopathological hypotheses posited to account for the unilateral appearance of chilblains in the event of paralysis include decreased blood flow to the paralysed limb, imbalance in neuromodulators, dysfunction of the autonomous nervous system, cutaneous atrophy with hypertrophy of underlying soft tissues, and finally, hypoesthesia aggravating the trophic disorders.

Interactions of the immune and sensory nervous systems in atopy

A striking feature underlying all atopic disorders, such as asthma, atopic dermatitis, and food allergy, is the presence of pathologic sensory responses, reflexes, and behaviors. These symptoms, exemplified by chronic airway irritation and cough, chronic itch and scratching, as well as gastrointestinal discomfort and dysfunction, are often cited as the most debilitating aspects of atopic disorders. Emerging studies have highlighted how the immune system shapes the scope and intensity of sensory responses by directly modulating the sensory nervous system. Additionally, factors produced by neurons have demonstrated novel functions in propagating atopic inflammation at barrier surfaces. In this review, we highlight new studies that have changed our understanding of atopy through advances in characterizing the reciprocal interactions between the immune and sensory nervous systems.

Asymmetric Acral Spared Phenomenon Related to Systemic Anticancer Therapies

We have observed three patients on anticancer therapies presenting with asymmetric acral spared phenomenon and found six identical cases in the literature. All of them had common features, an alteration of the peripheral nerves affecting a limb unilaterally that was spared by a hand-foot syndrome or hand-foot skin reaction. A drug-induced neurotropic effect sounds logical for developing such alterations with specific chemotherapeutic agents (taxanes, cap-ecitabine), while we have not found good explanations concerning the multikinase inhibitor sorafenib nor the topo isomerase inhibitor adriamycin. Nevertheless, we know that clinical manifestations of many inflammatory diseases need intact neural components.

The male beard hair and facial skin - challenges for shaving

The challenge of shaving is to cut the beard hair as closely as possible to the skin without unwanted effects on the skin. To achieve this requires the understanding of beard hair and male facial skin biology as both, the beard hair and the male facial skin, contribute to the difficulties in obtaining an effective shave without shaving-induced skin irritation. Little information is available on the biology of beard hairs and beard hair follicles. We know that, in beard hairs, the density, thickness, stiffness, as well as the rates of elliptical shape and low emerging angle, are high and highly heterogeneous. All of this makes it challenging to cut it, and shaving techniques commonly employed to overcome these challenges include shaving with increased pressure and multiple stroke shaving, which increase the probability and extent of shaving-induced skin irritation. Several features of male facial skin pose problems to a perfect shave. The male facial skin is heterogeneous in morphology and roughness, and male skin has a tendency to heal slower and to develop hyperinflammatory pigmentation. In addition, many males exhibit sensitive skin, with the face most often affected. Finally, the hair follicle is a sensory organ, and the perifollicular skin is highly responsive to external signals including mechanical and thermal stimulation. Perifollicular skin is rich in vasculature, innervation and cells of the innate and adaptive immune system. This makes perifollicular skin a highly responsive and inflammatory system, especially in individuals with sensitive skin. Activation of this system, by shaving, can result in shaving-induced skin irritation. Techniques commonly employed to avoid shaving-induced skin irritation include shaving with less pressure, pre- and post-shave skin treatment and to stop shaving altogether. Recent advances in shaving technology have addressed some but not all of these issues. A better understanding of beard hairs, beard hair follicles and male facial skin is needed to develop novel and better approaches to overcome the challenge of shaving. This article covers what is known about the physical properties of beard hairs and skin and why those present a challenge for blade and electric shaving, respectively.

The Regulation of Immunological Processes by Peripheral Neurons in Homeostasis and Disease

The nervous system and the immune system are the principal sensory interfaces between the internal and external environment. They are responsible for recognizing, integrating, and responding to varied stimuli, and have the capacity to form memories of these encounters leading to learned or 'adaptive' future responses. We review current understanding of the cross-regulation between these systems. The autonomic and somatosensory nervous systems regulate both the development and deployment of immune cells, with broad functions that impact on hematopoiesis as well as on priming, migration, and cytokine production. In turn, specific immune cell subsets contribute to homeostatic neural circuits such as those controlling metabolism, hypertension, and the inflammatory reflex. We examine the contribution of the somatosensory system to autoimmune, autoinflammatory, allergic, and infectious processes in barrier tissues and, in this context, discuss opportunities for therapeutic manipulation of neuro-immune interactions.

Linear psoriasis following the typical distribution of the sciatic nerve

BACKGROUND

Some studies suggest that the nervous system plays a role in the onset of psoriasis and psoriasis flares including the symmetry of lesions, sparing of denervated skin and the role of stress in inducing lesions.

MAIN OBSERVATIONS

We describe an unusual case of psoriasis occurring in the same distribution as sciatic pain from a prolapsed intervertebral disc. The patient, a 45-year-old man with plaque psoriasis was treated with ustekinumab for 104 weeks, at a standard dose. During the eight month of therapy he developed an asymptomatic linear eruption on the left lower extremity along the distribution of the sciatic nerve. On examination, erythematous scaly plaques were noted. Histopathology confirmed the diagnosis of psoriasis. The treatment was continued and clobetasol proprionate 0.05% cream was added. At week 12 after the eruption, the patient reported a pain radiating through the buttock and posterior left leg during jogging. Magnetic resonance imaging showed lumbar disc herniation with compression of the L5-S1 spinal nerve roots. The patient stopped running and the psoriasis spontaneously receded, in a slow but complete fashion, without any local treatment.

CONCLUSION

There is substantial evidence that nerves play a key role in the pathogenesis of psoriasis. We hypothesized that local TNF-alpha, neuropeptides and nerve growth factor, which are produced by nerve root compression, played a critical role in this case of psoriasis onset in an area of pain from a bulging lumbar intervertebral disc. To our knowledge, a correlation of psoriasis and nerve root compression has not been described previously.