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Resumen Introduccion La enfermedad por coronavirus-19 (COVID-19) se ha relacionado con multiples sintomas: respiratorios, tromboticos, neurologicos, digestivos o cutaneos. Estos ultimos se han clasificado en 5 tipos: lesiones acroisquemicas, lesiones vesiculares, erupcion urticarial, exantema maculopapular o lesiones livedoides. Sin embargo, se han descrito mucho menos las alteraciones orales asociadas a la COVID-19. Pacientes y metodos Presentamos un estudio transversal realizado durante abril del 2020 en el Hospital de Campana de IFEMA examinando la mucosa oral de 666 pacientes con COVID-19. Resultados En total, 78 pacientes (11,7%) presentaron alteraciones en la mucosa oral. La mas frecuente fue papilitis lingual transitoria anterior en forma de U (11,5%) asociada o no a edema lingual (6,6%); estomatitis aftosa (6,9%), mucositis (3,9%) glositis con depapilacion en parches (3,9%), boca urente (5,3%), lengua saburral (1,6%) y enantema (0,5%). La mayoria referia disgeusia asociada. Conclusion La cavidad oral se puede alterar por la enfermedad COVID-19, el edema lingual con papilitis lingual transitoria en forma de U o la glositis con depapilacion en parches son los signos encontrados con mayor frecuencia, al igual que la sensacion de ardor en la cavidad oral o boca urente. Otras manifestaciones orales que se pueden asociar a la COVID-19 son mucositis con o sin aftas o el enantema. Todos pueden ser signos clave para un diagnostico de esta enfermedad.

Segmental stiff skin syndrome (SSSS) is a rare genetic connective tissue disease, which is often misdiagnosed. High-frequency ultrasonography can represent a useful clinical adjunct in the differential diagnosis of this condition, in conjunction with the clinical and histopathological findings. Treatment options are limited and evidence is scarce. We present the clinical, sonographic and histological features of 5 paediatric patients diagnosed at our institution and we discuss their response to treatment.

Background Coronavirus disease 19 (COVID-19) has many manifestations, including respiratory, thrombotic, neurologic, digestive, and cutaneous ones. Cutaneous manifestations have been classified into 5 clinical patterns: acro-ischemic (pseudo-chilblain), vesicular, urticarial, maculopapular, and livedoid. Oral manifestations have also been reported, but much less frequently. Patients and methods We performed a cross-sectional study in which we examined the oral mucosa of 666 patients with COVID-19 at the IFEMA field hospital in Madrid in April 2020. Results Seventy-eight patients (11.7%) had changes involving the oral mucosa. The most common were transient anterior U-shaped lingual papillitis (11.5%) accompanied or not by tongue swelling (6.6%), aphthous stomatitis (6.9%), a burning sensation in the mouth (5.3%), mucositis (3.9%), glossitis with patchy depapillation (3.9%), white tongue (1.6%), and enanthema (0.5%). Most of the patients also reported taste disturbances. Conclusions COVID-19 also manifests in the oral cavity. The most common manifestations are transient U-shaped lingual papillitis, glossitis with patchy depapillation, and burning mouth syndrome. Mucositis with or without aphthous ulcers or enanthema may also be observed. Any these findings may be key clues to a diagnosis of COVID-19.

Coronavirus disease 2019 (Covid-2019) has been associated with several cutaneous manifestations(1-3). A temporary field hospital was implemented during the pandemic peak in Madrid, Spain, to attend COVID-19 patients with mild to moderate pneumonia.

Background The cutaneous manifestations of COVID-19 disease are poorly characterized. Objectives To describe the cutaneous manifestations of COVID-19 disease and to relate them to other clinical findings. Methods We carried out a nationwide case collection survey of images and clinical data. Using a consensus we described five clinical patterns. We later described the association of these patterns with patient demographics, the timing in relation to symptoms of the disease, the severity and the prognosis. Results The lesions may be classified as acral areas of erythema with vesicles or pustules (pseudo-chilblain) (19%), other vesicular eruptions (9%), urticarial lesions (19%), maculopapular eruptions (47%) and livedo or necrosis (6%). Vesicular eruptions appear early in the course of the disease (15% before other symptoms). The pseudo-chilblain pattern frequently appears late in the evolution of the COVID-19 disease (59% after other symptoms), while the rest tend to appear with other symptoms of COVID-19. The severity of COVID-19 shows a gradient from less severe disease in acral lesions to more severe in the latter groups. The results are similar for confirmed and suspected cases, in terms of both clinical and epidemiological findings. Alternative diagnoses are discussed but seem unlikely for the most specific patterns (pseudo-chilblain and vesicular). Conclusions We provide a description of the cutaneous manifestations associated with COVID-19 infection. These may help clinicians approach patients with the disease and recognize cases presenting with few symptoms. What is already known about this topic? Previous descriptions of cutaneous manifestations of COVID-19 were case reports and mostly lacked illustrations. What does this study add? We describe a large, representative sample of patients with unexplained skin manifestations and a diagnosis of COVID-19, using a consensus method to define morphological patterns associated with COVID-19. We describe five clinical patterns associated with different patient demographics, timing and prognosis, and provide illustrations of these patterns to allow for easy recognition.

Wet wrap therapy (WWT) consists of topical steroids administered under a layer of wet cotton bandages or garments. Several trials with WWT have reported promising results in atopic dermatitis (AD). However, no systematic review and meta-analysis on its efficacy and safety has been published. Our objective was to conduct a systematic review of the literature on WWT in AD to assess its efficacy and safety. We included randomized controlled trials among patients of all ages with a diagnosis of AD based on predefined criteria or made by a dermatologist. Electronic searches were performed from 1970 to 30 March 2016 in the Cochrane Central Register of Controlled Trials, MEDLINE, Embase and the World Health Organization International Clinical Trials Registry. Selection of studies and data extraction were performed independently by two researchers, and discrepancies were resolved by consensus. Six trials comparing WWT with topical steroids in children or adults with AD were included. Sample sizes ranged from 19 to 51 patients. Results on clinical severity and quality of life were reported incompletely and proved heterogeneous across studies. A nonsignificant tendency to increased risk of mild skin infections was observed in those treated with WWT (pooled relative risk 6·35, 95% confidence interval 0·83-48·55). The overall grade of quality of evidence for the efficacy and safety outcomes was low. In conclusion, the evidence that WWT is more effective than conventional treatment with topical steroids in AD is of low quality. Further clinical trials should establish the efficacy of WWT in AD.

Severe delayed drug-induced skin reactions in children are not common but potentially serious. This article describes aspects concerning the etiology, pathogenesis and clinical manifestations of these processes; it presents three paediatric cases, namely STS (Steven Johnson Syndrome), TEN (toxic epidermal necrolysis), probably related to amoxicillin/clavulanate and ibuprofen and DRESS (a drug reaction with eosinophilia and systemic symptoms) secondary to phenytoin; and in relation to them, the diagnosis and the treatment of these processes are discussed and reviewed. The AGEP (acute generalised exanthematous pustulosis) is also reviewed. The aetiological diagnosis of severe non-immediate reactions is difficult, and the value of current allergological testing is not well defined in these cases. Diagnosis is based on clinical history, the empirical risk of drugs to trigger SJS/TEN or DRESS, and the in vivo and in vitro testing of the suspect drug. Skin biopsy confirms that the clinical diagnosis and delayed hypersensitivity tests, especially the patch test and the lymphoblastic transformation test (LTT), may be important to confirm the aetiological diagnosis, in our cases emphasising the latter. These diseases can be life threatening (especially DRESS and TEN) and/or have a high rate of major complications or sequelae (SJS/TEN). The three cases described progressed well without sequelae. All were treated with corticosteroids, which is the most currently accepted treatment although the effect has not been clearly demonstrated.

Idiopathic facial aseptic granuloma is a typical childhood disease characterized by the presence of one or more asymptomatic nodules on the cheek. Although pathogenesis remains unclear, the disease is thought to be a type of childhood rosacea. It resolves spontaneously, yet it could be confused with other lesions that require treatment. We present clinical and ultrasound findings and outcome from 3 new cases. In 2 cases, the lesion presented as childhood rosacea. Ultrasound revealed a characteristic pattern, with variations depending on the stage of development. High-frequency ultrasound can facilitate the differential diagnosis and thus obviate unnecessary biopsy or excision.

Amyloid is a proteinaceous material that is deposited in the tissues in a large variety of clinical contexts; in the skin it can be found with or without concomitant systemic disease. Primary localized cutaneous amyloidosis encompasses those amyloidoses restricted to the skin without involvement of other systems. The most common forms within this group are macular and lichen amyloidosis. Nodular amyloidosis is extremely rare, and there are notable differences in clinical presentation, prognosis, histology, and pathogenesis between this entity and the macular and lichenoid variants. We report a new case of nodular primary localized cutaneous amyloidosis with disseminated plaques and nodules in which no systemic disease developed in the 3 years following the appearance of the lesions.

Closed-loop or feedback controlled ratchets are Brownian motors that operate using information about the state of the system. For these ratchets, we compute the power output and we investigate its relation with the information used in the feedback control. We get analytical expressions for one-particle and few-particle flashing ratchets, and we find that the maximum power output has an upper bound proportional to the information. In addition, we show that the increase of the power output that results from changing the optimal open-loop ratchet to a closed-loop ratchet also has an upper bound that is linear in the information., LaTeX, 6 pages, 4 figures, improved version to appear in Eur. Phys. J. B

Heparin use is associated with various cutaneous reactions, with the most common being immune-mediated skin lesions and bleeding complications. In this review, we compile the dermatological side-effects of heparin reported in the literature, and provide a clear approach to their adequate management.

Feedback or closed-loop control allows dynamical systems to increase their performance up to a limit imposed by the second law of thermodynamics. It is expected that within this limit, the system performance increases as the controller uses more information about the system. However, despite the relevant progresses made recently, a general and complete formal development to justify this statement using information theory is still lacking. We present here the state-of-the-art and the main open problems that include aspects of the redundancy of correlated operations of feedback control and the continuous operation of feedback control. Complete answers to these questions are required to firmly establish the thermodynamics of feedback controlled systems. Other relevant open questions concern the implications of the theoretical results for the limitations in the performance of feedback controlled flashing ratchets, and for the operation and performance of nanotechnology devices and biological systems., LaTeX, 10 pages, 2 figures. Improved version to appear in Entropy

Invasive vascular procedures have good efficacy and safety profiles and are now widely used for the diagnosis and treatment of many cardiovascular disorders. However, they do have potential complications that can occasionally be life-threatening. We present a new case of infectious pseudoaneurysm following percutaneous transluminal coronary angioplasty and complicated by septic emboli to the skin. It is a rare condition characterized by persistent bacteremia, sepsis of unknown origin, and regional septic emboli. Histopathology of the skin lesions typically reveals gram-positive coccobacilli and septic vasculitis. The condition carries a significant morbidity and mortality, making early diagnosis essential. Both cholesterol and septic emboli should be considered in the differential diagnosis of skin lesions after invasive vascular procedures.

We compute the entropy reduction in feedback controlled systems due to the repeated operation of the controller. This was the lacking ingredient to establish the thermodynamics of these systems, and in particular of Maxwell's demons. We illustrate some of the consequences of our general results by deriving the maximum work that can be extracted from isothermal feedback controlled systems. As a case example, we finally study a simple system that performs an isothermal information-fueled particle pumping., Comment: LaTeX, 7 pages, 2 figures. Improved version to appear in Phys. Rev. E

We investigate the different regimes that emerge when a periodic driving force, the rocking force, acts on a collective feedback flashing ratchet. The interplay of the rocking and the feedback control gives a rich dynamics with different regimes presenting several unexpected novel features. In particular, we show that for both the one-particle ratchet and the collective version of the ratchet an appropriate rocking increases the flux. This mechanism gives the maximum flux that has been achieved in a ratchet device without an a priori bias., Comment: LaTeX, 8 pages, 8 figures. To appear in Phys. Rev. E

Amyloid is a proteinaceous material that is deposited in the tissues in a large variety of clinical contexts; in the skin it can be found with or without concomitant systemic disease. Primary localized cutaneous amyloidosis encompasses those amyloidoses restricted to the skin without involvement of other systems. The most common forms within this group are macular and lichen amyloidosis. Nodular amyloidosis is extremely rare, and there are notable differences in clinical presentation, prognosis, histology, and pathogenesis between this entity and the macular and lichenoid variants. We report a new case of nodular primary localized cutaneous amyloidosis with disseminated plaques and nodules in which no systemic disease developed in the 3 years following the appearance of the lesions.

Feedback flashing ratchets are thermal rectifiers that use information on the state of the system to operate the switching on and off a periodic potential. We discuss different strategies for this operation with the aim of maximizing the net flux of particles in the collective version of a flashing ratchet consisting on N overdamped Brownian particles. We show the optimal protocols for the one-particle ratchet and for the collective ratchet with an infinite number of particles. Finally we comment on the unsolved problem of the optimal strategy for any other number of particles., LaTeX, 5 pages, 2 figures. Presented at the 5th International Conference on Unsolved Problems on Noise (UPON'08). Selected to appear in Journal of Statistical Mechanics (JSTAT)

Feedback flashing ratchets are thermal rectifiers that use information on the state of the system to operate the switching on and off of a periodic potential. They can induce directed transport even with symmetric potentials thanks to the asymmetry of the feedback protocol. We investigate here the dynamics of a feedback flashing ratchet when the asymmetry of the ratchet potential and of the feedback protocol favor transport in opposite directions. The introduction of a time delay in the control strategy allows one to nontrivially tune the relative relevance of the competing asymmetries leading to an interesting dynamics. We show that the competition between the asymmetries leads to a current reversal for large delays. For small ensembles of particles current reversal appears as the consequence of the emergence of an open-loop like dynamical regime, while for large ensembles of particles it can be understood as a consequence of the stabilization of quasiperiodic solutions. We also comment on the experimental feasibility of these feedback ratchets and their potential applications., Comment: LaTeX, 7 pages, 6 figures

Closed-loop or feedback control ratchets use information about the state of the system to operate with the aim of maximizing the performance of the system. In this paper we investigate the effects of a time delay in the feedback for a protocol that performs an instantaneous maximization of the center-of-mass velocity. For the one and the few particle cases the flux decreases with increasing delay, as an effect of the decorrelation of the present state of the system with the information that the controller uses, but the delayed closed-loop protocol succeeds to perform better than its open-loop counterpart provided the delays are smaller than the characteristic times of the Brownian ratchet. For the many particle case, we also show that for small delays the center-of-mass velocity decreases for increasing delays. However, for large delays we find the surprising result that the presence of the delay can improve the performance of the nondelayed feedback ratchet and the flux can attain the maximum value obtained with the optimal periodic protocol. This phenomenon is the result of the emergence of a dynamical regime where the presence of the delayed feedback stabilizes one quasiperiodic solution or several (multistability), which resemble the solutions obtained in the so-called threshold protocol. Our analytical and numerical results point towards the feasibility of an experimental implementation of a feedback controlled ratchet that performs equal or better than its optimal open-loop version., Comment: LaTeX, 11 pages, 13 figures. Material from arXiv:0706.4466 added. Improved version to appear in Phys Rev E

Incontinentia pigmenti is a rare, dominantly X-linked genodermatosis characterized by multisystemic involvement that is lethal prenatally in the majority of affected males and shows great clinical variability when it is expressed in women. Recently it has been shown that mutations of the gene NEMO/IKK-g located in Xq28 cause the expression of the disease, being only one mutation responsible for approximately 80 % of the cases. The diagnosis of incontinentia pigmenti is performed based on clinical features and family history with the support of histological findings. Nevertheless, as the gene responsible for the phenotype of the disease has been identified, a genetic study may be employed for doubtful cases. We report three cases of this entity (two women and one man) in different clinical stages of development that show the broad clinical spectrum we may encounter in the clinic.

We study a feedback control version of the flashing Brownian ratchet, in which the application of the flashing potential depends on the state of the particles to be controlled. Taking the view that the ratchet acts as a Maxwell's demon, we study the relationship that exists between the performance of the demon as a rectifier of random motion and the amount of information gathered by the demon through measurements. In the context of a simple measurement model, we derive analytic expressions for the flux induced by the feedback ratchet when acting on one particle and a few particles, and compare these results with those obtained with its open-loop version, which operates without information. Our main finding is that the flux in the feedback case has an upper bound proportional to the square-root of the information. Our results provide a quantitative analysis of the value of information in feedback ratchets, as well as an effective description of imperfect or noisy feedback ratchets that are relevant for experimental applications., Comment: LaTeX, 13 pages, 2 figures

Acrocyanosis is an infrequent entity characterized by persistent and symmetrical erythrocyanotic discoloration of the hands, feet and face, which is not preceded by episodes of previous paleness. Acrocyanosis can be secondary to a variety of underlying causes, but is uncommon as a form of presentation of systemic sclerosis. We present a new clinical case of this disease and discuss its etiopathogenic, clinical, diagnostic and therapeutic characteristics; in addition to, we seek to distinguish this term from others that might be confused in the literature.

We study the threshold control protocol for a collective flashing ratchet. In particular, we analyze the dependence of the current on the values of the thresholds. We have found analytical expressions for the small threshold dependence both for the few and for the many particle case. For few particles the current is a decreasing function of the thresholds, thus, the maximum current is reached for zero thresholds. In contrast, for many particles the optimal thresholds have a nonzero finite value. We have numerically checked the relation that allows to obtain the optimal thresholds for an infinite number of particles from the optimal period of the periodic protocol. These optimal thresholds for an infinite number of particles give good results for many particles. In addition, they also give good results for few particles due to the smooth dependence of the current up to these threshold values., LaTeX, 10 pages, 7 figures, improved version to appear in Phys. Rev. E

La acrocianosis es un cuadro clínico caracterizado por una coloración azul violácea persistente y simétrica de zonas acras, principalmente manos y pies, que no está precedida por episodios de palidez previos. Es una entidad que puede asociarse a diversas causas subyacentes, pero es infrecuente que lo haga como forma de debút de una esclerosis sistémica progresiva. Se presenta a continuación un nuevo caso de esta patología y se comentan sus características etiopatogénicas, clínicas y diagnósticas más relevantes además de un intento de diferenciar este término de otros con los que existe confusión en la literatura.

The effects of the initial temperature in the out of equilibrium quantum field dynamics in the presence of an homogeneous external field are investigated. We consider an initial thermal state of temperature T for a constant external field J. A subsequent sign flip of the external field, J to -J, gives rise to an out of equilibrium nonperturbative quantum field dynamics. The dynamics is studied here for the symmetry broken lambda(Phi^2)^2 scalar N component field theory in the large N limit. We find a dynamical effective potential for the expectation value that helps to understand the dynamics. The dynamics presents two regimes defined by the presence or absence of a temporal trapping close to the metastable equilibrium position of the potential. The two regimes are separated by a critical value of the external field that depends on the initial temperature. The temporal trapping is shorter for larger initial temperatures or larger external fields. Parametric resonances and spinodal instabilities amplify the quantum fluctuations in the field components transverse to the external field. When there is a temporal trapping this is the main mechanism that allows the system to escape from the metastable state for large N. Subsequently backreaction stops the growth of the quantum fluctuations and the system enters a quasiperiodic regime., Comment: LaTeX, 19 pages, 12 .eps figures, improved version to appear in Phys Rev D