Which Ultrasound Characteristics Predict Lymphatic Spread of Papillary Thyroid Cancer?

INTRODUCTION: The 2015 American Thyroid Association guidelines recommend lymph node mapping US in patients with definitive cytological evidence of thyroid cancer. Suspicious lymph node features on imaging including enlarged size (>1 cm in any dimension), architectural distortion, loss of fatty hilum, and microcalcifications often prompt evaluation with fine needle aspiration. There is no universally agreed upon model for determining which ultrasound characteristics most strongly correlate with metastatic disease. METHODS: A retrospective review of patients with confirmed papillary thyroid cancer (PTC) undergoing lymph node mapping ultrasound from 2013 to 2019 was performed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value were calculated for each individual ultrasound characteristic as well as for characteristic combinations. RESULTS: Data from 119 lymph nodes were included. Malignant lymph nodes were more likely to be enlarged (71% versus 61%, P < 0.001) and to have each individual suspicious feature. Loss of fatty hilum had the highest sensitivity (89%) but was not specific (19%) for metastatic disease. Architectural distortion was found to have the highest specificity (87%). A combination of the four features was found to have higher specificity (97%) and PPV (88%) than any individual feature or combination of two/three features. CONCLUSIONS: A combination of four sonographic features correlates with metastatic PTC to lymph nodes and has the highest specificity and PPV for malignancy. A risk stratification model based on these features may lead to better classification of ultrasound findings in PTC patients with concern for nodal metastases.

Intensity-dependent gamma electrical stimulation regulates microglial activation, reduces beta-amyloid load, and facilitates memory in a mouse model of Alzheimer's disease.

BACKGROUND: Gamma sensory stimulation may reduce AD-specific pathology. Yet, the efficacy of alternating electrical current stimulation in animal models of AD is unknown, and prior research has not addressed intensity-dependent effects. METHODS: The intensity-dependent effect of gamma electrical stimulation (GES) with a sinusoidal alternating current at 40 Hz on Aß clearance and microglia modulation were assessed in 5xFAD mouse hippocampus and cortex, as well as the behavioral performance of the animals with the Morris Water Maze. RESULTS: One hour of epidural GES delivered over a month significantly (1) reduced Aß load in the AD brain, (2) increased microglia cell counts, decreased cell body size, increased length of cellular processes of the Iba1 + cells, and (3) improved behavioral performance (learning & memory). All these effects were most pronounced when a higher stimulation current was applied. CONCLUSION: The efficacy of GES on the reduction of AD pathology and the intensity-dependent feature provide guidance for the development of this promising therapeutic approach.

Safety and Effectiveness of Expandable Intravertebral Implant Use for Thoracolumbar Burst Fractures.

PURPOSE: To determine the safety and effectiveness of an expandable intravertebral implant (Spinejack; Stryker, Kalamazoo, Michigan) as a treatment option for patients with thoracolumbar spine burst fractures without fracture-related neurologic deficit. MATERIALS AND METHODS: Imaging studies before and after expandable intravertebral implantation and medical records of 33 patients, 11 (33.3%) men and 22 (66.6%) women with an overall mean age of 71.7 years ± 8.3, were reviewed for 60 thoracolumbar Magerl Type A3 injuries secondary to osteoporosis, trauma, or malignancy. The mean follow-up time was 299 days. RESULTS: Implantation of an expandable intravertebral device resulted in a statistically significant reduction in bone fragment retropulsion (mean ± SD, 0.64 mm ± 16.4; P < .001), reduction in the extent of canal compromise (mean, 5.5%; P < .001), increased central canal diameter (mean ± SD, 0.71 mm ± 1.3; P < .001), and restoration of vertebral body height, with a mean increase of 5.0 mm (P < .001). However, the implantation did not result in a statistically significant kyphosis reduction (mean, 1.38°; P = .10). All patients except for 1 reported improvement in pain after surgery, with a mean improvement of 1.54 on a 4-point pain scale (P < .001). No clinically significant adverse events were reported. CONCLUSIONS: This study suggests that expandable intravertebral device implantation is a safe and effective treatment for thoracolumbar vertebral burst fractures in patients without fracture-related neurologic deficit. Although implantation did not result in a statistically significant reduction in kyphotic angle, it offered significant improvement in pain, vertebral body height, fracture fragment retropulsion, and central canal diameter compromise.

The curious case of the Zzz's.

Excessive daytime sleepiness is a common presenting symptom that may present a diagnostic challenge for the sleep medicine clinician. We present a case of an adolescent female with excessive daytime sleepiness and "sleep attacks" who was evaluated using a 2-week sleep log, wrist actigraphy, baseline polysomnogram, and Multiple Sleep Latency Test. Multiple Sleep Latency Test results noted a short mean sleep latency without sleep onset rapid eye movement periods, concerning for possible central disorders of hypersomnolence. However, actigraphy data noted a habitual bedtime of midnight or later, resulting in less than recommended total sleep time for her age on weekdays with extended sleep periods on the weekends. The most unique actigraphy finding was exposure to ambient light throughout most overnight sleep periods. When actigraphy results were discussed with the patient, she revealed recent onset of severe anxiety with fear of sleeping in the dark. This case highlights the importance of thorough clinical evaluation, and careful interpretation of objective tests, when evaluating for causes of excessive daytime sleepiness. CITATION: Dang L, Kanney ML, Hsu DP. The curious case of the Zzz's. J Clin Sleep Med. 2023;19(5):1009-1012.

Distinct features of the host-parasite interactions between nonadherent and adherent Trichomonas vaginalis isolates.

Cytoadherence of Trichomonas vaginalis to human vaginal epithelial cells (hVECs) was previously shown to involve surface lipoglycans and several reputed adhesins on the parasite. Herein, we report some new observations on the host-parasite interactions of adherent versus nonadherent T. vaginalis isolates to hVECs. The binding of the TH17 adherent isolate to hVECs exhibited an initial discrete phase followed by an aggregation phase inhibited by lactose. T. vaginalis infection immediately induced surface expression of galectin-1 and -3, with extracellular amounts in the spent medium initially decreasing and then increasing thereafter over the next 60 min. Extracellular galectin-1 and -3 were detected on the parasite surface but only the TH17 adherent isolate could uptake galectin-3 via the lysosomes. Only the adherent isolate could morphologically transform from the round-up flagellate with numerous transient protrusions into a flat amoeboid form on contact with the solid surface. Cytochalasin D challenge revealed that actin organization was essential to parasite morphogenesis and cytoadherence. Real-time microscopy showed that parasite exploring and anchoring on hVECs via the axostyle may be required for initial cytoadherence. Together, the parasite cytoskeleton behaviors may collaborate with cell surface adhesion molecules for cytoadherence. The nonadherent isolate migrated faster than the adherent isolate, with motility transiently increasing in the presence of hVECs. Meanwhile, differential histone acetylation was detected between the two isolates. Also, TH17 without Mycoplasma symbiosis suggests that symbiont might not determine TH17 innate cytoadherence. Our findings regarding distinctive host-parasite interactions of the isolates may provide novel insights into T. vaginalis infection.

Social impairment and snoring: a unique presentation of pediatric Chiari I malformation.

Symptomatic progression of Chiari malformation type 1 (CM-1) can be difficult to recognize in children because of the slow progressive nature of the disorder and highly varied neurological symptoms. We present a case of an obese 11-year-old girl seeking an evaluation of snoring. Progressive social impairment and academic difficulties were also endorsed. The past medical history was remarkable for absence seizures at an earlier age with an incidental finding of CM-1 on brain imaging. No headaches, vision changes, or swallowing dysfunction were endorsed in the acute presentation. The patient underwent a polysomnogram, which revealed the unexpected finding of severe central sleep apnea. Magnetic resonance imaging of the brain revealed further herniation of the cerebellar tonsils and a cervical syrinx, which was not present on initial imaging. Posterior fossa decompression resulted in the successful resolution of symptoms. It was postulated that the social impairment and academic problems were manifestations of CM-1. There are no current standard protocols for disease surveillance of pediatric CM-1. Annual polysomnograms may serve as a useful tool. CITATION: Kanney ML, Spear J, Hsu DP. Social impairment and snoring: a unique presentation of pediatric Chiari I malformation. J Clin Sleep Med. 2022;18(12):2867-2870.

Galectin-3 facilitates cell-to-cell HIV-1 transmission by altering the composition of membrane lipid rafts in CD4 T cells.

Galectin-3 (GAL3) is a ß-galactoside-binding lectin expressed in CD4 T cells infected with human immunodeficiency virus-1 (HIV-1). GAL3 promotes HIV-1 budding by associating with ALIX and Gag p6. GAL3 has been shown to localize in membrane lipid rafts in dendritic cells and positively regulate cell migration. HIV-1 spreads between T cells by forming supramolecular structures (virological synapses [VSs]), whose integrity depends on lipid rafts. Here, we addressed the potential role of GAL3 in cell-to-cell transmission of HIV-1 in CD4 T cells. GAL3 expressed in donor cells was more important for facilitating HIV-1 cell-to-cell transfer than GAL3 expressed in target cells. GAL3 was found to be co-transferred with Gag from HIV-1-positive donor to HIV-1-negative target T cells. HIV-1 infection induced translocation of GAL3 together with Gag to the cell-cell interfaces and colocalize with GM1, where GAL3 facilitated VS formation. GAL3 regulated the coordinated transfer of Gag and flotillin-1 into plasma membrane fractions. Finally, depletion of GAL3 reduced the cholesterol levels in membrane lipid rafts in CD4 T cells. These findings provide evidence that endogenous GAL3 stimulates lipid raft components and facilitates intercellular HIV-1 transfer among CD4 T cells, offering another pathway by which GAL3 regulates HIV-1 infection. These findings may inform the treatment of HIV-1 infection based on targeting GAL3 to modulate lipid rafts.

Social media (SoMe) enhances exposure of dermatology articles.

Social media (SoMe) refers to a variety of virtual platforms used to enhance sharing of information. To evaluate the influence of SoMe with regards to views and downloads of published dermatology articles, we conducted a retrospective study from July 2020-March 2021 examining articles published on Instagram and Twitter under Dermatology Online Journal (DOJ) accounts and compared these with type-matched and issue-matched articles that were not posted on social media. During this time period, 163 total articles of the three types used for social media (Case Report, Case Presentation, and Photo Vignette) were published in DOJ and 15 were promoted via SoMe. Utilization of SoMe demonstrated a significant (P<0.0001) positive effect with regards to both views (175.5±16.4) and downloads (31.5±4.0) over matched articles not published on SoMe. Similar trends illustrating the positive effect of SoMe on readership have been previously observed in the field of dermatology as well as other medical specialties. Most direct accessions to articles arrived via Instagram rather than Twitter, diverging from previous studies on SoMe use in medical journals. Social media, in particular Instagram, can be a successful platform to enhance the exposure of peer-reviewed medical information.

Indispensable role of Galectin-3 in promoting quiescence of hematopoietic stem cells.

Hematopoietic stem cells (HSCs) in adult bone marrow (BM) are usually maintained in a state of quiescence. The cellular mechanism coordinating the balance between HSC quiescence and differentiation is not fully understood. Here, we report that galactose-binding lectin-3 (galectin-3; Gal-3) is upregulated by Tie2 or Mpl activation to maintain quiescence. Conditional overexpression of Gal-3 in mouse HSCs under the transcriptional control of Tie2 or Vav1 promoters (Gal-3 Tg) causes cell cycle retardation via induction of p21. Conversely, the cell cycle of long-term repopulating HSCs (LT-HSCs) in Gal-3-deficient (Gal-3-/-) mice is accelerated, resulting in their exhaustion. Mechanistically, Gal-3 regulates p21 transcription by forming a complex with Sp1, thus blocking cell cycle entry. These results demonstrate that Gal-3 is a negative regulator of cell-cycling in HSCs and plays a crucial role in adult hematopoiesis to prevent HSC exhaustion.

Galectin-7 downregulation in lesional keratinocytes contributes to enhanced IL-17A signaling and skin pathology in psoriasis.

Psoriasis is a chronic inflammatory skin disease characterized by inflammatory cell infiltration, as well as hyperproliferation of keratinocytes in skin lesions, and is considered a metabolic syndrome. We found that the expression of galectin-7 is reduced in skin lesions of patients with psoriasis. IL-17A and TNF-α, 2 cytokines intimately involved in the development of psoriatic lesions, suppressed galectin-7 expression in human primary keratinocytes (HEKn cells) and the immortalized human keratinocyte cell line HaCaT. A galectin-7 knockdown in these cells elevated the production of IL-6 and IL-8 and enhanced ERK signaling when the cells were stimulated with IL-17A. Galectin-7 attenuated IL-17A-induced production of inflammatory mediators by keratinocytes via the microRNA-146a/ERK pathway. Moreover, galectin-7-deficient mice showed enhanced epidermal hyperplasia and skin inflammation in response to intradermal IL-23 injection. We identified fluvastatin as an inducer of galectin-7 expression by connectivity map analysis, confirmed this effect in keratinocytes, and demonstrated that fluvastatin attenuated IL-6 and IL-8 production induced by IL-17A. Thus, we validate a role of galectin-7 in the pathogenesis of psoriasis, in both epidermal hyperplasia and keratinocyte-mediated inflammatory responses, and formulate a rationale for the use of statins in the treatment of psoriasis.

Galectin-3 as a Therapeutic Target for NSAID-Induced Intestinal Ulcers.

Non-steroidal anti-inflammatory drugs (NSAIDs) induce ulcers in the gastrointestinal tract, including the stomach and small intestine. NSAID-induced gastric ulcers can be prevented by taking acid-neutralizing/inhibitory drugs and cytoprotective agents. In contrast, there are no medicines to control NSAID-induced small intestinal ulcers, which are accompanied by a mucosal invasion of bacteria and subsequent activation of immune cells. Galectin-3 (Gal3), an endogenous lectin, has anti-microbial and pro-inflammatory functions. In the small intestine, since Gal3 is highly expressed in epithelial cells constitutively and macrophages inducibly, the Gal3 level can affect microbiota composition and macrophage activation. We hypothesized that the modulation of Gal3 expression could be beneficial in NSAID-induced intestinal ulcers. Using Gal3 knockout (Gal3KO) mice, we determined whether Gal3 could be a therapeutic target in NSAID-induced intestinal ulcers. Following the administration of indomethacin, an NSAID, we found that small intestinal ulcers were less severe in Gal3KO mice than in wild-type (WT) mice. We also found that the composition of intestinal microbiota was different between WT and Gal3KO mice and that bactericidal antibiotic polymyxin B treatment significantly suppressed NSAID-induced ulcers. Furthermore, clodronate, a macrophage modulator, attenuated NSAID-induced ulcers. Therefore, Gal3 could be an exacerbating factor in NSAID-induced intestinal ulcers by affecting the intestinal microbiota population and macrophage activity. Inhibition of Gal3 may be a therapeutic strategy in NSAID-induced intestinal ulcers. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT03832946.

A monocyte-keratinocyte-derived co-culture assay accurately identifies efficacies of BET inhibitors as therapeutic candidates for psoriasiform dermatitis.

BACKGROUND: Bromodomain and extra-terminal (BET) proteins perform key roles in epigenetic control of gene expression that is involved in inflammatory conditions, including psoriasiform dermatitis (PsD). Predicting which (of many potential available BET inhibitors) will be effective in vivo is challenging. OBJECTIVE: We determine if a novel in vitro assay that includes two critical cell types involved in human psoriasis can predict the therapeutic potential of specific BET inhibitors in vivo. METHODS: An in vitro model consisting of U-937 and HaCaT cell co-culture was created to screen small molecule BET antagonists for inhibition of cutaneous inflammatory genes. Efficacious BET inhibitors were tested in a mouse imiquimod (IMQ)-induced PsD model. RESULTS: In the co-culture system, HaCaT cells exhibited a marked increase in the secretion of a characteristic set of proinflammatory and Th17-associated cytokines. Of the ten commercially-available small molecules targeting BET proteins assayed, most compounds exhibited inhibitory functions at 1 µM against inflammatory activation, but responded variably at lower concentrations. OTX015, a typical representative for most of the compounds, barely inhibited the inflammatory reactions at 0.1 µM. By contrast, ABBV075 was effective in concentrations as low as 0.01 µM. While oral administration OTX015 in IMQ-treated mice reduced disease severity, ABBV075 equally decreased the symptoms and molecular and cellular severity markers at one-tenth of the minimal dosing required for OTX015. CONCLUSION: In vitro screening system combined with an in vivo animal model, can serve as a convenient pre-clinical screening tool for the selection of BET inhibitors (and possibly other drugs) that may have clinical potential in psoriasis therapy.

Risk of Distal Embolization From tPA (Tissue-Type Plasminogen Activator) Administration Prior to Endovascular Stroke Treatment.

BACKGROUND AND PURPOSE: In large artery occlusion stroke, both intravenous (IV) tPA (tissue-type plasminogen activator) and endovascular stroke treatment (EST) are standard-of-care. It is unknown how often tPA causes distal embolization, in which a procedurally accessible large artery occlusion is converted to a more distal and potentially inaccessible occlusion. METHODS: We analyzed data from a decentralized stroke telemedicine program in an integrated healthcare delivery system covering 21 hospitals, with 2 high-volume EST centers. We captured all cases sent for EST and examined the relationship between IV tPA administration and the rate of distal embolization, the rate of target recanalization (modified Treatment in Cerebral Infarction scale 2b/3), clinical improvement before EST, and short-term and long-term clinical outcomes. RESULTS: Distal embolization before EST was quite common (63/314 [20.1%]) and occurred more often after IV tPA before EST (57/229 [24.9%]) than among those not receiving IV tPA (6/85 [7.1%]; P<0.001). Distal embolization was associated with an inability to attempt EST: after distal embolization, 26/63 (41.3%) could not have attempted EST because of the new clot location, while in cases without distal embolization, only 8/249 (3.2%) were unable to have attempted EST (P<0.001). Among patients who received IV tPA, 13/242 (5.4%) had sufficient symptom improvement that a catheter angiogram was not performed; 6/342 (2.5%) had improvement to within 2 points of their baseline NIHSS. At catheter angiogram, 2/229 (0.9%) of patients who had received tPA had complete recanalization without distal embolization. Both IV tPA and EST recanalization were associated with improved long-term outcome. CONCLUSIONS: IV tPA administration before EST for large artery occlusion is associated with distal embolization, which in turn may reduce the chance that EST can be attempted and recanalization achieved. At the same time, some IV tPA-treated patients show symptomatic improvement and complete recanalization. Because IV tPA is associated with both distal embolization and improved long-term clinical outcome, there is a need for prospective clinical trials testing the net benefit or harm of IV tPA before EST.

Intracranial alternating current stimulation facilitates neurogenesis in a mouse model of Alzheimer's disease.

BACKGROUND: Neurogenesis is significantly impaired in the brains of both human patients and experimental animal models of Alzheimer's disease (AD). Although deep brain stimulation promotes neurogenesis, it is an invasive technique that may damage neural circuitry along the path of the electrode. To circumvent this problem, we assessed whether intracranial electrical stimulation to the brain affects neurogenesis in a mouse model of Alzheimer's disease (5xFAD). METHODS AND RESULTS: We used Ki67, Nestin, and doublecortin (DCX) as markers and determined that neurogenesis in both the subventricular zone (SVZ) and hippocampus were significantly reduced in the brains of 4-month-old 5xFAD mice. Guided by a finite element method (FEM) computer simulation to approximately estimate current and electric field in the mouse brain, electrodes were positioned on the skull that were likely to deliver stimulation to the SVZ and hippocampus. After a 4-week program of 40-Hz intracranial alternating current stimulation (iACS), neurogenesis indicated by expression of Ki67, Nestin, and DCX in both the SVZ and hippocampus were significantly increased compared to 5xFAD mice who received sham stimulation. The magnitude of neurogenesis was close to the wild-type (WT) age-matched unmanipulated controls. CONCLUSION: Our results suggest that iACS is a promising, less invasive technique capable of effectively stimulating the SVZ and hippocampus regions in the mouse brain. Importantly, iACS can significantly boost neurogenesis in the brain and offers a potential treatment for AD.

A Small Molecule CCR2 Antagonist Depletes Tumor Macrophages and Synergizes with Anti-PD-1 in a Murine Model of Cutaneous T-Cell Lymphoma (CTCL).

Tumor-associated macrophages (TAMs) recruited from blood monocytes are key in establishing an immunosuppressive tumor microenvironment (TME) for the support of tumor growth. We hypothesize that blocking monocyte trafficking (through the inhibition of specific chemokine receptors) into skin can positively affect tumor development. Herein, the authors examined the effects of oral administration of a small molecule inhibitor for CCR2, CCR2i, which blocks CCR2-mediated chemotaxis of monocytes in a syngeneic mouse T-cell lymphoma in skin. Following CCR2i administration, the depletion of macrophages was achieved as early as 2 days after tumor initiation in ear TME. Quantitative real-time PCR detected an increase in the levels of immune stimulatory inflammatory cytokines, for example, IFN-γ and IL-12, in CCR2i- versus vehicle-treated mice. Within 2 weeks, the tumors from the control groups attained the maximum size, whereas CCR2i-treated mice exhibited much smaller tumor sizes and weights. Immunohistochemistry revealed that CCR2i-treated tumors possessed considerably more CD8+ T cells, which demonstrated their essential role in CCR2i-induced tumor inhibition. Finally, the combination of anti-programmed cell death protein 1 with CCR2i considerably increased the efficacy of tumor eradication related to the activation of IFN-γ-producing CD8 T cells. Our findings provide strong evidence that the CCR2i, particularly in combination with an immune checkpoint inhibitor, reduces tumor growth and is a potential future treatment option for cutaneous T-cell lymphomas.

Prevalence of Pulmonary Hypertension in Pediatric Patients With Obstructive Sleep Apnea and a Cardiology Evaluation: A Retrospective Analysis.

STUDY OBJECTIVES: Pulmonary hypertension (PH) has been reported as a serious complication of obstructive sleep apnea (OSA) in children; however, estimated prevalence rates vary widely (zero to 85%). The purpose of this study is to determine the prevalence of PH in children with OSA and identify factors that may predict an increased PH risk in children with OSA. METHODS: A retrospective review of all pediatric beneficiaries (88,058) in the San Antonio Military Health System with a diagnosis of OSA and a clinical evaluation by a pediatric cardiologist. OSA severity and nadir oxygen saturation were recorded from overnight polysomnography. Reason for referral, comorbid disorders, echocardiogram results, and cardiac diagnoses were obtained from cardiology records. RESULTS: OSA was identified in 2,020 pediatric patients (2.3%). A pediatric cardiology consultation was reported for 296 patients with OSA. After excluding 95 patients for incorrect OSA diagnoses, incomplete data, or OSA treatment before cardiology evaluation, 163 patients were included in the final analysis. A diagnosis of PH was found in 3 patients with OSA (1.8%). Two of these patients had obesity, and all three had comorbid cardiac disorders. CONCLUSIONS: Prevalence of PH in pediatric patients with OSA is low and none of the patients with PH had severe OSA. Current guidelines recommend PH screening in patients with severe OSA, yet OSA severity may not accurately predict risk. Factors evaluated in this study did not demonstrate an increased PH risk; additional research is necessary to improve screening in pediatric patients with OSA. CITATION: Burns AT, Hansen SL, Turner ZS, Aden JK, Black AB, Hsu DP. Prevalence of pulmonary hypertension in pediatric patients with obstructive sleep apnea and a cardiology evaluation: a retrospective analysis. J Clin Sleep Med. 2019;15(8):1081-1087.

Using a machine learning approach to determine the space group of a structure from the atomic pair distribution function.

A method is presented for predicting the space group of a structure given a calculated or measured atomic pair distribution function (PDF) from that structure. The method utilizes machine learning models trained on more than 100 000 PDFs calculated from structures in the 45 most heavily represented space groups. In particular, a convolutional neural network (CNN) model is presented which yields a promising result in that it correctly identifies the space group among the top-6 estimates 91.9% of the time. The CNN model also successfully identifies space groups for 12 out of 15 experimental PDFs. Interesting aspects of the failed estimates are discussed, which indicate that the CNN is failing in similar ways as conventional indexing algorithms applied to conventional powder diffraction data. This preliminary success of the CNN model shows the possibility of model-independent assessment of PDF data on a wide class of materials.

Reconciling modern machine-learning practice and the classical bias-variance trade-off.

Breakthroughs in machine learning are rapidly changing science and society, yet our fundamental understanding of this technology has lagged far behind. Indeed, one of the central tenets of the field, the bias-variance trade-off, appears to be at odds with the observed behavior of methods used in modern machine-learning practice. The bias-variance trade-off implies that a model should balance underfitting and overfitting: Rich enough to express underlying structure in data and simple enough to avoid fitting spurious patterns. However, in modern practice, very rich models such as neural networks are trained to exactly fit (i.e., interpolate) the data. Classically, such models would be considered overfitted, and yet they often obtain high accuracy on test data. This apparent contradiction has raised questions about the mathematical foundations of machine learning and their relevance to practitioners. In this paper, we reconcile the classical understanding and the modern practice within a unified performance curve. This "double-descent" curve subsumes the textbook U-shaped bias-variance trade-off curve by showing how increasing model capacity beyond the point of interpolation results in improved performance. We provide evidence for the existence and ubiquity of double descent for a wide spectrum of models and datasets, and we posit a mechanism for its emergence. This connection between the performance and the structure of machine-learning models delineates the limits of classical analyses and has implications for both the theory and the practice of machine learning.