Cold water exposure and vaso-occlusive crises in sickle cell anemia

Cold exposure induces vaso-occlusion and pain in sickle mice that depend on complement activation

Vaso-occlusive pain episodes (VOE) cause severe pain in patients with sickle cell disease (SCD). Vaso-occlusive events promote ischemia/reperfusion pathobiology that activates complement. We hypothesized that complement activation is linked to VOE. We used cold to induce VOE in the Townes sickle homozygous for hemoglobin S (HbSS) mouse model and complement inhibitors to determine whether anaphylatoxin C5a mediates VOE. We used a dorsal skinfold chamber to measure microvascular stasis (vaso-occlusion) and von Frey filaments applied to the plantar surface of the hind paw to assess mechanical hyperalgesia in HbSS and control Townes mice homozygous for hemoglobin A (HbAA) mice after cold exposure at 10°C/50°F for 1 hour. Cold exposure induced more vaso-occlusion in nonhyperalgesic HbSS mice (33%) than in HbAA mice (11%) or HbSS mice left at room temperature (1%). Cold exposure also produced mechanical hyperalgesia as measured by paw withdrawal threshold in HbSS mice compared with that in HbAA mice or HbSS mice left at room temperature. Vaso-occlusion and hyperalgesia were associated with an increase in complement activation fragments Bb and C5a in plasma of HbSS mice after cold exposure. This was accompanied by an increase in proinflammatory NF-κB activation and VCAM-1 and ICAM-1 expression in the liver. Pretreatment of nonhyperalgesic HbSS mice before cold exposure with anti-C5 or anti-C5aR monoclonal antibodies (mAbs) decreased vaso-occlusion, mechanical hyperalgesia, complement activation, and liver inflammatory markers compared with pretreatment with control mAb. Anti-C5 or -C5aR mAb infusion also abrogated mechanical hyperalgesia in HbSS mice with ongoing hyperalgesia at baseline. These findings suggest that C5a promotes vaso-occlusion, pain, and inflammation during VOE and may play a role in chronic pain.

Determinants of severity in sickle cell disease

Sickle cell disease is a very variable condition, with outcomes ranging from death in childhood to living relatively symptom free into the 8^th decade. Much of this variability is unexplained. The co-inheritance of α thalassaemia and factors determining HbF levels significantly modify the phenotype, but few other significant genetic variants have been identified, despite extensive studies. Environmental factors are undoubtedly important, with socio-economics and access to basic medical care explaining the huge differences in outcomes between many low- and high-income countries. Exposure to cold and windy weather seems to precipitate acute complications in many people, although these effects are unpredictable and vary with geography. Many studies have tried to identify prognostic factors which can be used to predict outcomes, particularly when applied in infancy. Overall, low haemoglobin, low haemoglobin F percentage and high reticulocytes in childhood are associated with worse outcomes, although again these effects are fairly weak and inconsistent.

Phenotypic variation in sickle cell disease: the role of beta globin haplotype, alpha thalassaemia and fetal haemoglobin in HbSS

INTRODUCTION

The haematological and clinical feature vary markedly between the different genotypes of sickle cell disease. Even within the single genotype of homozygous sickle cell disease (HbSS), there is marked variability which is presumed to result from interacting genetic and environmental factors.

AREAS COVERED

The classification of the different genotypes of sickle cell disease with approximate prevalence at birth in different communities and some of the major clinical and haematological differences. This assessment includes three potential genetic factors influencing haematology and clinical outcome in HbSS, the beta globin haplotype, alpha thalassaemia and persistence of fetal haemoglobin (HbF).

EXPERT OPINION

The author is a clinician with experience of sickle cell disease primarily in Jamaica but also in Greece, Uganda, Saudi Arabia and India. It is therefore necessarily an account of clinical data and does not address current debates on molecular mechanisms. Most data derive from Jamaica where efforts have been made to reduce any symptomatic bias by long term follow-up of patients all over the island and further reduced by a cohort study based on newborn screening which has been in operation for over 48 years.

Topical Vapocoolant-Associated Vaso-occlusive Event in a 10-year-old with Sickle Cell Disease

Vapocoolant sprays are convenient forms of cold temperature analgesia. These sprays may not be suitable for all patients with particular concern for patients with sickle cell disease. To prevent any further cases from occurring, we propose adding a more specific cautionary statement to the manufacturer guidelines. We also hope that medical personnel can help patients with sickle cell avoid topical and environmental cold temperature triggers for sickle vaso-occlusive pain and reduce the suffering in this rare disease.

Opioid Prescription Filling Trends Among Children with Sickle Cell Disease After the Release of State-Issued Guidelines on Pain Management

OBJECTIVE

To assess the impact of Ohio's 2012, 2013, and 2016 opioid prescribing guidelines on opioid and nonsteroidal anti-inflammatory drug (NSAID) prescription filling and health care utilization for pain among children with sickle cell disease (SCD).

DESIGN

Quasi-experimental retrospective cohort study.

SETTING

Ohio Medicaid claims data from August 2011 to August 2016.

SUBJECTS

Medicaid beneficiaries under age 19 years with SCD.

METHODS

Interrupted time series analyses comparing population-level rates of opioids and NSAID prescriptions filled, standardized amounts of opioids dispensed, and acute health care utilization for pain before and after release of each guideline.

RESULTS

In our cohort of 1,505 children with SCD, there was a temporary but significant decrease in the opioid filling rate (-2.96 prescriptions per 100 children, P = 0.01) and in the amount of opioids dispensed (-31.39 milligram morphine equivalents per filled prescription, P < 0.001) after the 2013 guideline but a temporary but significant increase in the opioid filling rate (7.44 prescriptions per 100 children, P < 0.001) and in the amount of opioids dispensed (72.73 mg morphine equivalents per filled prescription, P < 0.001) after the 2016 guideline. The NSAID filling rate did not significantly change after any of the guidelines. Acute health care utilization rates for pain after the 2016 guideline were similar to those before the 2013 guideline (rate ratio = 1.04, P = 0.63).

CONCLUSIONS

Our results suggest that Ohio's 2013 and 2016 guidelines were associated with significant but nonsustained changes in opioid prescription filling among children with SCD. Additional studies are needed to confirm that opioid guidelines have a sustained impact on excessive opioid prescribing, filling, and misuse.

Progressive vasoconstriction with sequential thermal stimulation indicates vascular dysautonomia in sickle cell disease

Persons with sickle cell disease (SCD) exhibit subjective hypersensitivity to cold and heat perception in experimental settings, and triggers such as cold exposure are known to precipitate vaso-occlusive crises by still unclear mechanisms. Decreased microvascular blood flow (MBF) increases the likelihood of vaso-occlusion by increasing entrapment of sickled red blood cells in the microvasculature. Because those with SCD have dysautonomia, we anticipated that thermal exposure would induce autonomic hypersensitivity of their microvasculature with an increased propensity toward vasoconstriction. We exposed 17 patients with SCD and 16 control participants to a sequence of predetermined threshold temperatures for cold and heat detection and cold and heat pain via a thermode placed on the right hand. MBF was measured on the contralateral hand by photoplethysmography, and cardiac autonomic balance was assessed by determining heart rate variability. Thermal stimuli at both detection and pain thresholds caused a significant decrease in MBF in the contralateral hand within seconds of stimulus application, with patients with SCD showing significantly stronger vasoconstriction (P = .019). Furthermore, patients with SCD showed a greater progressive decrease in blood flow than did the controls, with poor recovery between episodes of thermal stimulation (P = .042). They had faster vasoconstriction than the controls (P = .033), especially with cold detection stimulus. Individuals with higher anxiety also experienced more rapid vasoconstriction (P = .007). Augmented vasoconstriction responses and progressive decreases in perfusion with repeated thermal stimulation in SCD are indicative of autonomic hypersensitivity in the microvasculature. These effects are likely to increase red cell entrapment in response to clinical triggers such as cold or stress, which have been associated with vaso-occlusive crises in SCD.

Review/overview of pain in sickle cell disease

Sickle cell disease (SCD) is a highly complex inherited disorder of hemoglobin structure. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of the disease. Its manifestations could be acute, chronic, nociceptive, neuropathic that could occur singly or in various combinations. Pain continues to be the major factor of SCD phenotypic complications and the most common cause of admissions to the Emergency Department and/or the hospital. Although progress has been made in understanding the pathophysiology of SCD as well as in developing curative therapies such as hematopoietic stem cell transplantation and gene therapy, effective pain management continues to lag behind. Palliative therapies continue to be the major approach to the management of SCD and its complications. The advent of hydroxyurea made partial success in preventing the frequency of vaso-occlusive crises and l-glutamine awaits post-trial confirmation of benefits. The search for additional pharmacotherapeutic agents that could be used singly or in combination with hydroxyurea and/or l-glutamine awaits their dawn hopefully in the near future. The purpose of this review is to describe the various manifestations of SCD, their pathophysiology and their current management. Recent impressive advances in understanding the pathophysiology of pain promise the determination of agents that could replace or minimize the use of opioids.

Children and adolescents with sickle cell disease have worse cold and mechanical hypersensitivity during acute painful events

Sickle cell disease (SCD) pain associates with cold temperature and touch. Patients and murine models with SCD have baseline thermal and mechanical pain. In SCD mice, the baseline hypersensitivity is exacerbated by experimental vaso-occlusive crises. We hypothesized that patients with SCD will similarly experience increased hypersensitivity to thermal and mechanical stimuli during acute painful events compared with baseline health. We conducted a prospective study of 24 patients with SCD aged 7 to 19 years. Patients underwent quantitative sensory testing to thermal (cold/heat) and mechanical stimuli on the thenar eminence of the nondominant hand (glabrous skin) and the lateral dorsum of the foot (hairy skin) during baseline health and within 48 hours of hospitalization for acute pain. Primary outcomes were changes in: (1) cold pain threshold (°C), (2) heat pain threshold (°C), and (3) mechanical pain threshold (g). Median age was 10.5 (interquartile range [IQR] 9-14.8) years, 67% were females, and 92% were on hydroxyurea. Patients with SCD had increased cold pain sensitivity in the hand during hospitalization compared with baseline (25.2°C [IQR 18.4-27.5°C] vs 21.3°C [IQR 4.9-26.2°C]; P = 0.011) and increased mechanical pain sensitivity in the foot during hospitalization (0.32 g [IQR 0.09-1.1 g] vs 1.7 g [IQR 0.4-8.3 g]; P = 0.003). There were no differences in heat pain sensitivity. The increased cold (P = 0.02) and mechanical (P = 0.0016) pain sensitivity during hospitalization persisted after adjusting for age, sex, hydroxyurea use, opioid consumption, and numeric pain score. Thus, cold and mechanical pain is significantly worse during an acute SCD painful event as compared to baseline health in patients with SCD.

Sickle cell disease: Clinical presentation and management of a global health challenge

Sickle cell disease is an autosomal recessive, multisystem disorder, characterised by chronic haemolytic anaemia, painful episodes of vaso-occlusion, progressive organ failure and a reduced life expectancy. Sickle cell disease is the most common monogenetic disease, with millions affected worldwide. In well-resourced countries, comprehensive care programs have increased life expectancy of sickle cell disease patients, with almost all infants surviving into adulthood. Therapeutic options for sickle cell disease patients are however, still scarce. Predictors of sickle cell disease severity and a better understanding of pathophysiology and (epi)genetic modifiers are warranted and could lead to more precise management and treatment. This review provides an extensive summary of the pathophysiology and management of sickle cell disease and encompasses the characteristics, complications and current and future treatment options of the disease.

Sensitization of nociceptors by prostaglandin E2-glycerol contributes to hyperalgesia in mice with sickle cell disease

Pain is a characteristic feature of sickle cell disease (SCD), 1 of the most common inherited diseases. Patients may experience acute painful crises as well as chronic pain. In the Berkley transgenic murine model of SCD, HbSS-BERK mice express only human hemoglobin S. These mice share many features of SCD patients, including persistent inflammation and hyperalgesia. Cyclooxygenase-2 (COX-2) is elevated in skin, dorsal root ganglia (DRG), and spinal cord in HbSS-BERK mice. In addition to arachidonic acid, COX-2 oxidizes the endocannabinoid 2-arachidonoylglycerol (2-AG) to produce prostaglandin E₂ (PGE₂)-glycerol (PGE₂-G); PGE₂-G is known to produce hyperalgesia. We tested the hypotheses that PGE₂-G is increased in DRGs of HbSS-BERK mice and sensitizes nociceptors (sensory neurons that respond to noxious stimuli), and that blocking its synthesis would decrease hyperalgesia in HbSS-BERK mice. Systemic administration of R-flurbiprofen preferentially reduced production of PGE₂-G over that of PGE₂ in DRGs, decreased mechanical and thermal hyperalgesia, and decreased sensitization of nociceptors in HbSS-BERK mice. The same dose of R-flurbiprofen had no behavioral effect in HbAA-BERK mice (the transgenic control), but local injection of PGE₂-G into the hind paw of HbAA-BERK mice produced sensitization of nociceptors and hyperalgesia. Coadministration of a P2Y6 receptor antagonist blocked the effect of PGE₂-G, indicating that this receptor is a mediator of pain in SCD. The ability of R-flurbiprofen to block the synthesis of PGE₂-G and to normalize levels of 2-AG suggests that R-flurbiprofen may be beneficial to treat pain in SCD, thereby reducing the use of opioids to relieve pain.

Key Components of Pain Management for Children and Adults with Sickle Cell Disease

Sickle cell disease pain manifests as severe acute pain episodes and a debilitating chronic pain syndrome. Acute pain episodes are the most common reason for health care use; however, acute pain episodes are also frequently managed at home. Chronic pain syndrome develops in 30% to 40% of individuals with sickle cell disease, with an increasing incidence and severity with age. We review the critical aspects of pain management that are integral to the comprehensive approach to sickle cell disease pain and are rooted in the biopsychosocial model. The review focuses on opioid pharmacology and psychosocial comorbidities.

AAAPT Diagnostic Criteria for Acute Sickle Cell Disease Pain

Acute pain episodes are the most common complication in patients with sickle cell disease (SCD). Classically attributed to vaso-occlusion, recent insights suggest that chronic pain may also contribute to the pathogenesis of acute pain episodes, which adds complexity to their diagnosis and management. A taxonomy, or classification system, for acute pain in patients with SCD would aid research efforts and enhance clinical care. To meet this need, the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks public-private partnership with the U.S. Food and Drug Administration, the American Pain Society, and the American Academy of Pain Medicine formed the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks-American Pain Society-American Academy of Pain Medicine Pain Taxonomy initiative. One of the goals of this initiative was to develop taxonomies for acute pain disorders, including SCD. To accomplish this, a working group of experts in SCD and pain was convened. Based on available literature and expert opinion, the working group used a 5-dimenional structure (diagnostic criteria, common features, modulating factors, impact/functional consequences, and putative mechanisms) to develop an acute pain taxonomy that is specific to SCD. As part of this, a set of 4 diagnostic criteria, with 2 modifiers to account for the influence of chronic pain, are proposed to define the types of acute pain observed in patients with SCD. PERSPECTIVE: This article presents a taxonomy for acute pain in patients with SCD. This taxonomy could help to standardize definitions of acute pain in clinical studies of patients with SCD.

Neuronal transient receptor potential (TRP) channels and noxious sensory detection in sickle cell disease

Pain is the leading cause for hospitalization in patients with sickle cell disease (SCD). While the characteristics of SCD pain can vary widely between patients and between phases of the disease (e.g. vasoocclusive crisis pain vs. chronic pain), similar neuronal mechanisms likely underlie the various aspects of nociceptive processing. In the peripheral nervous system, small unmyelinated C fibers and lightly-myelinated Aδ fibers detect and transmit noxious stimuli. Both classes of neurons express members of the transient receptor potential (TRP) family, a group of ligand gated ion-channels that are activated by thermal, chemical, and mechanical stimuli. Promiscuous TRP channel family members are activated by a wide range of stimuli, many of which are dysregulated in patients with SCD and transgenic SCD mouse models. In 2011, our lab published the first report of TRP channel contributions to rodent SCD pain. Since that time, additional basic and clinical research efforts have investigated the genetic and biochemical status of TRP channels in SCD, placing particular focus on TRPV1. This review will discuss these advances and highlight the clinical SCD presentations that have not yet been studied, but which may be mediated by TRP channel activity.

The Bone Pain Crisis of Sickle Cell Disease and Malaria: Observations from Gujarat, India

BACKGROUND

Sickle cell disease is a common problem across central India, but its clinical features may differ from that in African populations. There is a need to define the features of sickle cell disease in India, and the current study addresses some features of the bone pain crisis.

OBJECTIVES

The objective of the study was to describe the epidemiology of the bone pain crisis of sickle cell disease in Gujarat and explore the relationship with infection by Plasmodium vivax.

MATERIALS AND METHODS

This was a prospective review of all admissions in patients with sickle cell disease to a private pediatric institution in Bardoli, Gujarat, in the year 2015. Hemoglobin electrophoresis of all patients was consistent with homozygous sickle cell disease, but family studies indicated that at least seven cases had the severe sickle cell-beta + thalassemia presumed to be the common IVS1-5G>C mutation. Clinical, hematological, and parasitological features were recorded.

RESULTS

There were 914 admissions among 654 patients who had between one and seven admissions. The bone pain crisis accounted for 763 (83%) of admissions and increased between July and October coinciding with the monsoon period. Blood smears were examined for malarial parasites in 811 admissions and were positive for P. vivax in 73% patients. There was no evidence that P. vivax infections varied with the cause of admission or increased during the monsoon period.

CONCLUSIONS

There was a high prevalence of P. vivax infection in hospital admissions of sickle cell patients, but the data did not support an etiological role in the bone pain crisis. A trial of malarial prophylaxis might determine its effect on the clinical features and outcome of sickle cell disease.

Secondhand Smoke Is an Important Modifiable Risk Factor in Sickle Cell Disease: A Review of the Current Literature and Areas for Future Research

Sickle cell disease (SCD) is an autosomal recessive hemoglobinopathy that causes significant morbidity and mortality related to chronic hemolytic anemia, vaso-occlusion, and resultant end-organ damage. Tobacco smoke exposure (TSE) through secondhand smoke exposure in people with SCD of all ages and through primary smoking in adolescents and adults is associated with significantly increased morbidity, with increased rates of emergency department visits and hospitalizations for painful vaso-occlusive crises and acute chest syndrome (ACS). Secondhand smoke is also associated with pulmonary function abnormalities in children with SCD who are already at risk for pulmonary function abnormalities on the basis of SCD. TSE is emerging as one of the few modifiable risk factors of SCD. This review discusses the current state of the evidence with respect to TSE and SCD morbidity, discusses potential mechanisms, and highlights current gaps in the evidence and future research directions.

Clinical Interpretation of Quantitative Sensory Testing as a Measure of Pain Sensitivity in Patients With Sickle Cell Disease

Patients with sickle cell disease (SCD) display significantly lower mean/median thermal and mechanical pain thresholds compared with controls. This suggests impaired pain sensitivity where stimuli produce exaggerated pain. Despite these mean/median differences, clinicians need to understand if patients meet criteria for impaired pain sensitivity. We defined thresholds for impaired cold, heat, and mechanical pain sensitivity in SCD patients. Using quantitative sensory testing (QST) we assessed cold, heat, and mechanical pain thresholds in SCD patients and African American controls aged 7 years and above. Impaired pain sensitivity was defined as: (1) cold pain threshold 1 SD above control median threshold; (2) heat pain threshold 1 SD below control median threshold; and (3) mechanical pain threshold 1 SD below control median threshold. Fifty-five SCD patients and 57 controls participated in this study. Impaired pain sensitivity thresholds were: (1) cold: 17.01°C, (2) heat: 43.91°C, and (3) mechanical: 4.42 g. Impaired cold pain sensitivity was the most common finding (63.6%), then heat (60%), and mechanical (38.2%). Impaired pain sensitivity to ≥1 testing modalities occurred in 81.8% of SCD patients. Determining impaired pain sensitivity thresholds increases clinical utility of QST. QST could be a screening tool to phenotype SCD pain, an outcome for pain interventional trials, or guide pain neurobiology investigations.

Environmental determinants of severity in sickle cell disease

Sickle cell disease causes acute and chronic illness, and median life expectancy is reduced by at least 30 years in all countries, with greater reductions in low-income countries. There is a wide spectrum of severity, with some patients having no symptoms and others suffering frequent, life-changing complications. Much of this variability is unexplained, despite increasingly sophisticated genetic studies. Environmental factors, including climate, air quality, socio-economics, exercise and infection, are likely to be important, as demonstrated by the stark differences in outcomes between patients in Africa and USA/Europe. The effects of weather vary with geography, although most studies show that exposure to cold or wind increases hospital attendance with acute pain. Most of the different air pollutants are closely intercorrelated, and increasing overall levels seem to correlate with increased hospital attendance, although higher concentrations of atmospheric carbon monoxide may offer some benefit for patients with sickle cell disease. Exercise causes some adverse physiological changes, although this may be off-set by improvements in cardiovascular health. Most sickle cell disease patients live in low-income countries and socioeconomic factors are undoubtedly important, but little studied beyond documenting that sickle cell disease is associated with decreases in some measures of social status. Infections cause many of the differences in outcomes seen across the world, but again these effects are relatively poorly understood. All the above factors are likely to account for much of the pathology and variability of sickle cell disease, and large prospective studies are needed to understand these effects better.

Autonomic responses to cold face stimulation in sickle cell disease: a time-varying model analysis

Sickle cell disease (SCD) is characterized by sudden onset of painful vaso-occlusive crises (VOC), which occur on top of the underlying chronic blood disorder. The mechanisms that trigger VOC remain elusive, but recent work suggests that autonomic dysfunction may be an important predisposing factor. Heart-rate variability has been employed in previous studies, but the derived indices have provided only limited univariate information about autonomic cardiovascular control in SCD. To circumvent this limitation, a time-varying modeling approach was applied to investigate the functional mechanisms relating blood pressure (BP) and respiration to heart rate and peripheral vascular resistance in healthy controls, untreated SCD subjects and SCD subjects undergoing chronic transfusion therapy. Measurements of respiration, heart rate, continuous noninvasive BP and peripheral vascular resistance were made before, during and after the application of cold face stimulation (CFS), which perturbs both the parasympathetic and sympathetic nervous systems. Cardiac baroreflex sensitivity estimated from the model was found to be impaired in nontransfused SCD subjects, but partially restored in SCD subjects undergoing transfusion therapy. Respiratory-cardiac coupling gain was decreased in SCD and remained unchanged by chronic transfusion. These results are consistent with autonomic dysfunction in the form of impaired parasympathetic control and sympathetic overactivity. As well, CFS led to a significant reduction in vascular resistance baroreflex sensitivity in the nontransfused SCD subjects but not in the other groups. This blunting of the baroreflex control of peripheral vascular resistance during elevated sympathetic drive could be a potential factor contributing to the triggering of VOC in SCD.

The use of neuropathic pain drugs in children with sickle cell disease is associated with older age, female sex, and longer length of hospital stay

Although neuropathic pain is increasingly recognized in sickle cell disease (SCD), it is unknown how neuropathic pain drugs are used in children with SCD. Thus, we investigated use of these drugs and hypothesized older age and female sex are associated with increased neuropathic drug use and the use of these drugs is associated with longer length of stay. We analyzed the Pediatric Health Information System (2004 to 2009) including all inpatient visits aged 0 to 18 years with any SCD-related (all genotypes) discharge diagnosis. To limit confounding we excluded psychiatric and seizure visits. Antiepileptics, tricyclic antidepressants, and selective serotonin reuptake inhibitors were drugs of interest. Generalized Estimating Equations determined the impact of age and sex on neuropathic drug use and the impact of neuropathic drug use on length of stay. We analyzed 53,557 visits; 2.9% received≥1 neuropathic drugs. The odds of receiving a neuropathic drug increased significantly with age (reference group, 0 to 4 y: 5 to 10, odds ratio [OR], 5.7; 11 to 14: OR, 12.5; 15 to 18: OR, 22.8; all P<0.0001] and female sex (OR, 1.5; P=0.001). Neuropathic drug use was associated with longer length of stay (risk ratio, 8.3; P<0.0001). Neuropathic drug use in children with SCD was associated with older age, female sex, and longer length of stay.

Cold hypersensitivity increases with age in mice with sickle cell disease

Sickle cell disease (SCD) is associated with acute vaso-occlusive crises that trigger painful episodes and frequently involves ongoing, chronic pain. In addition, both humans and mice with SCD experience heightened cold sensitivity. However, studies have not addressed the mechanism(s) underlying the cold sensitization or its progression with age. Here we measured thermotaxis behavior in young and aged mice with severe SCD. Sickle mice had a marked increase in cold sensitivity measured by a cold preference test. Furthermore, cold hypersensitivity worsened with advanced age. We assessed whether enhanced peripheral input contributes to the chronic cold pain behavior by recording from C fibers, many of which are cold sensitive, in skin-nerve preparations. We observed that C fibers from sickle mice displayed a shift to warmer (more sensitive) cold detection thresholds. To address mechanisms underlying the cold sensitization in primary afferent neurons, we quantified mRNA expression levels for ion channels thought to be involved in cold detection. These included the transient receptor potential melastatin 8 (Trpm8) and transient receptor potential ankyrin 1 (Trpa1) channels, as well as the 2-pore domain potassium channels, TREK-1 (Kcnk2), TREK-2 (Kcnk10), and TRAAK (Kcnk4). Surprisingly, transcript expression levels of all of these channels were comparable between sickle and control mice. We further examined transcript expression of 83 additional pain-related genes, and found increased mRNA levels for endothelin 1 and tachykinin receptor 1. These factors may contribute to hypersensitivity in sickle mice at both the afferent and behavioral levels.

Neuropathic pain in patients with sickle cell disease

BACKGROUND

Despite the suggestion of a neuropathic component to sickle cell disease (SCD) pain, there are minimal data on the systematic assessment of neuropathic pain in patients with SCD. Neuropathic pain is defined as pain primarily initiated by dysfunction of the peripheral or central nervous system.

PROCEDURE

In a cross-sectional study, we used the painDETECT questionnaire, a one-page validated neuropathic pain screening tool, to determine the presence of neuropathic pain in patients with SCD and to evaluate the relationship between neuropathic pain, age, and gender. We hypothesized that 20% of patients with SCD will experience neuropathic pain and that neuropathic pain will be associated with older age and female gender. The completed painDETECT questionnaire yields a total score between 0 and 38 (≥ 19 = definite neuropathic pain, 13-18 = probable neuropathic pain, ≤ 12 = no neuropathic pain). Scores ≥ 13 were designated as having evidence of neuropathic pain.

RESULTS

A total of 56 patients participated. Median age was 20.3 years and 77% were female. We found 37% of patients had evidence of neuropathic pain. Age was positively correlated with total score (r = 0.43; P = 0.001) suggesting older patients experience more neuropathic pain. Females had higher mean total scores (13 vs. 8.4; P = 0.04). Significantly more patients with neuropathic pain were taking hydroxyurea (90% vs. 59%; P = 0.015). Despite 37% of patients experiencing neuropathic pain, only 5% were taking a neuropathic pain drug.

CONCLUSIONS

Neuropathic pain exists in SCD. Valid screening tools can identify patients that would benefit from existing and future neuropathic pain therapies and could determine the impact of these therapies.

Current management of sickle cell anemia

Proper management of sickle cell anemia (SCA) begins with establishing the correct diagnosis early in life, ideally during the newborn period. The identification of affected infants by neonatal screening programs allows early initiation of prophylactic penicillin and pneumococcal immunizations, which help prevent overwhelming sepsis. Ongoing education of families promotes the early recognition of disease-released complications, which allows prompt and appropriate medical evaluation and therapeutic intervention. Periodic evaluation by trained specialists helps provide comprehensive care, including transcranial Doppler examinations to identify children at risk for primary stroke, plus assessments for other parenchymal organ damage as patients become teens and adults. Treatment approaches that previously highlighted acute vaso-occlusive events are now evolving to the concept of preventive therapy. Liberalized use of blood transfusions and early consideration of hydroxyurea treatment represent a new treatment paradigm for SCA management.

Patients with sickle cell disease have increased sensitivity to cold and heat

Sickle cell disease (SCD) pain is associated with colder temperatures and touch and described as "cold," "hot," and "shooting" suggesting hypersensitivity to tactile stimuli. Sickle mice exhibit hypersensitivity to thermal (cold, heat) and mechanical stimuli compared to controls. It is unknown whether humans experience this same hypersensitivity. Thus, we quantified thermal and mechanical sensitivity differences between patients with SCD and controls. Our primary hypothesis was that patients with SCD will exhibit hypersensitivity to thermal and mechanical stimuli compared to race-matched controls. Our secondary hypothesis was this hypersensitivity will be associated with older and female subjects, and with frequent pain and hemolysis in patients with SCD. A total of 55 patients and 57 controls ≥7 years completed quantitative sensory testing. Patients with SCD detected the sensation of cold and warm temperatures sooner as seen in their significantly lower median cold and heat detection thresholds [29.5°C vs. 28.6°C, P = 0.012 and 34.5°C vs. 35.3°C, P = 0.02] and experienced cold and heat pain sooner as seen in their significantly lower median cold and heat pain thresholds [21.1°C vs. 14.8°C, P = 0.01 and 42.7°C vs. 45.2°C, P = 0.04]. We found no mechanical threshold differences. Older age was associated with lower cold, heat, and mechanical pain thresholds in both groups. No association with pain, gender, or hemolysis was found. Patients with SCD exhibit hypersensitivity to thermal stimuli suggesting peripheral or central sensitization may exist and could contribute to SCD pain.

Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management

The sickle hemoglobin is an abnormal hemoglobin due to point mutation (GAG → GTG) in exon 1 of the β globin gene resulting in the substitution of glutamic acid by valine at position 6 of the β globin polypeptide chain. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of sickle cell disease in general and sickle cell anemia in particular. The disease itself is chronic in nature but many of its complications are acute such as the recurrent acute painful crises (its hallmark), acute chest syndrome, and priapism. These complications vary considerably among patients, in the same patient with time, among countries and with age and sex. To date, there is no well-established consensus among providers on the management of the complications of sickle cell disease due in part to lack of evidence and in part to differences in the experience of providers. It is the aim of this paper to review available current approaches to manage the major complications of sickle cell disease. We hope that this will establish another preliminary forum among providers that may eventually lead the way to better outcomes.

Cooling the crisis: therapeutic hypothermia after sickle cardiac arrest

OBJECTIVE

The management of patients with sickle-cell disease and cardiac arrest presents special challenges. Mild therapeutic hypothermia may improve survival and neurologic outcome after cardiac arrest, however, it may also precipitate sickling in patients with sickle-cell disease. Rigorous exchange transfusion may enable mild therapeutic hypothermia after cardiac arrest in patients with sickle-cell disease.

DESIGN

Case report.

SETTING

A 28-bed closed format intensive care unit in a university hospital.

PATIENT

A 41-yr-old man with a double-heterozygous sickle-cell β-0 thalassemia was admitted to the internal ward for acute chest syndrome. On the third day he developed cardiac arrest. Return of spontaneous circulation was achieved after 45 mins of full cardiopulmonary resuscitation.

INTERVENTIONS

Postcardiac arrest rigorous exchange transfusion and mild therapeutic hypothermia were applied.

MEASUREMENT AND MAIN RESULT

Erythrocytapheresis lowered the content of hemoglobin S to 5.6%, and therapeutic hypothermia was successfully maintained for 24 hrs without adverse events. After 2 critical weeks, the patient regained full consciousness.

CONCLUSION

Therapeutic hypothermia after cardiac arrest is feasible following rigorous exchange transfusion in patients with sickle-cell disease.

Effects of hydration and dehydration on blood rheology in sickle cell trait carriers during exercise

This study compared the hemorheological responses of a group of sickle cell trait (SCT) carriers with those of a control (Cont) group in response to 40 min of submaximal exercise (exercise intensity, 55% aerobic peak power) performed in two conditions: one with water offered ad libitum, i.e., the hydration (Hyd) condition, and one without water, i.e., the dehydration (Dehyd) condition. Blood and plasma viscosities, as well as red blood cell rigidity, were determined at rest, at the end of exercise, and at 2 h recovery with a cone plate viscometer at high shear rate and 37°C. The SCT and Cont groups lost 1 ± 0.7 and 1.6 ± 0.6 kg of body weight, respectively, in the Dehyd condition, indicating a significant effect of water deprivation compared with the Hyd condition, in which body weight remained unchanged. Plasma viscosity increased with exercise and returned to baseline during recovery independently of the group and condition. As previously demonstrated, resting blood viscosity was greater in the SCT carriers than in the Cont group. Blood viscosity increased by the end of exercise and returned to baseline at 2 h recovery in the Cont group in both conditions. The blood viscosity of SCT carriers did not change in response to exercise in the Dehyd condition and remained elevated at 2 h recovery. This extended hyperviscosity, in association with other biological changes induced by exercise, could be considered as a risk factor for exercise-related events in SCT carriers, similar to vasoocclusive crises, notably during the recovery. In contrast, the Hyd condition normalized the hyperviscosity and red blood cell rigidity of the SCT carriers, with blood viscosity values reaching the same lower values as those found in the Cont group during the recovery. Adequate hydration of SCT carriers should be strongly promoted to reduce the clinical risk associated with potential hyperviscosity complications.

Association between wind speed and the occurrence of sickle cell acute painful episodes: results of a case-crossover study

The role of the weather as a trigger of sickle cell acute painful episodes has long been debated. To more accurately describe the role of the weather as a trigger of painful events, we conducted a case-crossover study of the association between local weather conditions and the occurrence of painful episodes. From the Cooperative Study of Sickle Cell Disease, we identified 813 patients with sickle cell anaemia who had 3570 acute painful episodes. We found an association between wind speed and the onset of pain, specifically wind speed during the 24-h period preceding the onset of pain. Analysing wind speed as a categorical trait, showed a 13% increase (95% confidence interval: 3%, 24%) in odds of pain, when comparing the high wind speed to lower wind speed (P = 0.007). In addition, the association between wind speed and painful episodes was found to be stronger among men, particularly those in the warmer climate regions of the United States. These results are in agreement with another study that found an association between wind speed and hospital visits for pain in the United Kingdom, and lends support to physiological and clinical studies that have suggested that skin cooling is associated with sickle vasoocclusion and perhaps pain.

Bone and joint disease in sickle cell disease

Bone and joint disorders are the most common cause of chronic pain in patients who have sickle cell disease. The femoral head is the most common area of bone destruction in sickle cell patients, although other disease-related problems include avascular necrosis of the humeral head, changes in the thoracic and lumbar spine, infection with encapsulated organisms (Salmonella and Staphylococcus aureus are the most common), bone marrow disturbances, and dental effects. Complications can occur at any location: epiphyseal, metaphyseal, or diaphyseal. The location and the extensiveness of the problems determine the pain and structural damage. The hip joint is particularly vulnerable in sickle cell disease. This article highlights aspects of sickle cell disease that affect healthy bone and joint function and discusses treatment options.

Windy weather and low humidity are associated with an increased number of hospital admissions for acute pain and sickle cell disease in an urban environment with a maritime temperate climate

Sickle cell disease (SCD) is characterised by intermittent episodes of acute severe pain, related to vaso-occlusion. Environmental factors are thought to play an important role, and studies in tropical countries have suggested that cold and rainy seasons are associated with increased episodes of acute pain. We have studied retrospectively the number of admissions with acute pain and SCD to King's College Hospital, London, together with daily meteorological records collected locally. Data from 1400 d and 1047 separate admissions were analysed. Increased admissions were significantly associated with increased wind speed and low humidity, but showed no relationship to temperature, rainfall or barometric pressure. The strongest effect was for (maximum wind speed)/humidity, with 464 admissions on days in the lowest two quartiles of this parameter and 582 in the highest quartiles. The effect of high wind and low humidity is likely to be related to skin cooling.

Day-care management of sickle cell painful crisis in Jamaica: a model applicable elsewhere?

In the U.K. and the U.S.A., painful crises account for 80-90% of sickle-related hospital admissions, with average durations of 5-11 d. In Jamaica, many severe painful crises are managed in a day-care centre. Patients (n=1160) with homozygous sickle cell (SS) disease aged 18 years and over were registered with the clinic during a 1-year study period. Of these, 216 patients with 476 painful crises attended the day-care facility for a total of 686 d. Most patients (119 or 55.1%) had single crises and for most crises (338 or 71%), patients attended for only 1 d, when they were given bed rest, assurance, rehydration and analgesia. Patients with complicated painful crises were usually referred for admission after initial pain relief and the rest were monitored during the day. In the evening they were given the option of hospital admission or allowed home with oral analgesia. Hospital admission for complicated painful crises or inadequate pain relief occurred in 42 (8.8%) crises and home management in 434 (91.2%) crises. Of 186 patients initially selecting home management, 20% returned for further day-care and five (2.7%) died during subsequent admission for that painful crisis, one without other known complications, two with acute chest syndrome (one associated with Salmonella septicaemia), another with Salmonella septicaemia, and one with dengue haemorrhagic fever. With suitable oral analgesia, adequate education and support, the majority of severe painful crises in SS disease in Jamaica have been managed on an outpatient basis. This model of patient care may merit assessment in other communities where painful crises are a common clinical problem.

Hydroxyurea and sickle cell anemia. Clinical utility of a myelosuppressive "switching" agent. The Multicenter Study of Hydroxyurea in Sickle Cell Anemia

Painful crises in patients with sickle cell anemia are caused by vaso-occlusion and infarction. Occlusion of blood vessels depends on (at least) their diameter, the deformability of red cells, and the adhesion of blood cells to endothelium. Deoxygenated sickle cells are rigid because they contain linear polymers of hemoglobin S (Hb S); polymerization is highly concentration dependent, and dilution of Hb S by a nonsickling hemoglobin such as fetal hemoglobin (Hb F) would be expected to lead ultimately to a decrease in the frequency of painful crises. It might also be expected to decrease the severity of anemia, although the pathogenesis of anemia in sickle cell anemia (SS disease) is not clearly understood. Reversion to production of fetal rather than adult hemoglobin became practical with the discovery that HU was an orally effective and relatively safe "switching agent." Preliminary dose-ranging studies led to a double-blind randomized controlled clinical trial, the Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH), designed to test whether patients treated with HU would have fewer crises than patients treated with placebo. The MSH was not designed to assess the mechanism(s) by which a beneficial effect might be achieved, but it was hoped that observations made during the study might illuminate that question. The 2 MSH treatment groups were similar to each other and were representative of African-American patients with relatively severe disease. The trial was closed earlier than expected, after demonstration that median crisis rate was reduced by almost 50% (2.5 versus 4.5 crises per year) in patients assigned to HU therapy. Hospitalizations, episodes of chest syndrome, and numbers of transfusions were also lower in patients treated with HU. Eight patients died during the trial, and treatment was stopped in 53. There were no instances of alarming toxicity. Patients varied widely in their maximum tolerated doses, but it was not clear that all were taking their prescribed treatments. When crisis frequency was compared with various clinical and laboratory measurements, pretreatment crisis rate and treatment with HU were clearly related to crisis rate during treatment. Pretreatment laboratory measurements were not associated with crisis rates during the study in either treatment group. It was not clear that clinical improvement was associated with an increase in Hb F. Crisis rates of the 2 treatment groups became different within 3 months. Mean corpuscular volumes (MCVs) and the proportion of Hb F containing red cells (F cells) rose, and neutrophil and reticulocyte counts fell, within 7 weeks. When patients were compared on the basis of 2-year crisis rates, those with lower crisis rates had higher F-cell counts and MCVs and lower neutrophil counts. Neutrophil, monocyte, reticulocyte, and platelet counts were directly associated, and F cells and MCV were inversely associated, with crisis rates in 3-month periods. In multivariable analyses, there was strong evidence of independent association of lower neutrophil counts with lower crisis rates. F-cell counts were associated with crisis rate only in the first 3 months of treatment; MCV showed an association over longer periods of time. Overall, the evidence that decreased neutrophil counts played a role in reducing crisis rates was strong. Increased F cells or MCV and evidence of cytoreduction by HU were also associated with decreased crisis rates, but no definitive statement can be made regarding the mechanism of action of HU because the study was not designed to address that question. Future studies should be designed to explore the mechanism of action of HU, to identify the optimal dosage regimen, and to study the effect of HU when combined with other antisickling agents.