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Posttraumatic stress disorder(PTSD) is a severe anxiety disorder that can develop after exposure to any event that results in psychological trauma. This event may involve the threat of death to oneself or to someone else, or to one’s own or someone else’s physical, sexual, or psychological integrity,overwhelming the individual’s ability to cope. As an effect of psychological trauma, PTSD is less frequent and more enduring than the more commonly seen post traumatic stress (also known as acute stress response). Diagnostic symptoms for PTSD include re-experiencing the original trauma(s) through flashbacks or nightmares, avoidance of stimuli associated with the trauma, and increased arousal—such as difficulty falling or staying asleep, anger, and hypervigilance. Formal diagnostic criteria (both DSM-IV-TR and ICD-10) require that the symptoms last more than one month and cause significant impairment in social, occupational, or other important areas of functioning.
Classification
Posttraumatic stress disorder is classified as an anxiety disorder, characterized by aversive anxiety-related experiences, behaviors, and physiological responses that develop after exposure to a psychologically traumatic event (sometimes months after). Its features persist for longer than 30 days, which distinguishes it from the briefer acute stress disorder and are disruptive to all aspects of life.It has three sub-forms: acute, c
hronic, and delayed-onset.
Causes
Psychological trauma
PTSD is believed to be caused by experiencing any of a wide range of events which produces intense negative feelings of “fear, helplessness or horror”in the observer or participant. Sources of such feelings may include (but are not limited to):
- experiencing or witnessing childhood or adult physical, emotional, or sexual abuse;
- experiencing or witnessing physical assault, adult experiences of sexual assault, accidents, drug addiction, illnesses, medical complications;
- employment in occupations exposed to war (such as soldiers) or disaster (such as emergency service workers);
- getting a diagnosis of a life-threatening illness
Children or adults may develop PTSD symptoms by experiencing bullying or mobbing. Approximately 25% of children exposed to family violence can experience PTSD. Preliminary research suggests that child abuse may interact with mutations in a stress-related gene to increase the risk of PTSD in adults. However, being exposed to a traumatic experience doesn’t automatically indicate they will develop PTSD.It has been shown that the intrusive memories, such as flashbacks, nightmares, and the memories themselves, are greater contributors to the biological and psychological dimensions of PTSD than the event itself.These intrusive memories are mainly characterized by sensory episodes, rather than thoughts. People with PTSD have intrusive re-experiences of traumatic events which lack awareness of context and time. These episodes aggravate and maintain PTSD symptoms since the individual re-experiences trauma as if it was happening in the present moment.
Multiple studies show that parental PTSD and other posttraumatic disturbances in parental psychological functioning can, despite a traumatized parent’s best efforts, interfere with their response to their child as well as their child’s response to trauma. Parents with violence-related PTSD may, for example, inadvertently expose their children to developmentally inappropriate violent media due to their need to manage their own emotional dysregulation.Clinical findings indicate that a failure to provide adequate treatment to children after they suffer a traumatic experience, depending on their vulnerability and the severity of the trauma, will ultimately lead to PTSD symptoms in adulthood.
Neuroendocrinology
PTSD symptoms may result when a traumatic event causes an over-reactive adrenaline response, which creates deep neurological patterns in the brain. These patterns can persist long after the event that triggered the fear, making an individual hyper-responsive to future fearful situations. During traumatic experiences the high levels of stress hormones secreted suppress hypothalamic activity which may be a major factor towards the development of PTSD.
PTSD causes biochemical changes in the brain and body that differ from other psychiatric disorders such as major depression. Individuals diagnosed with PTSD respond more strongly to a dexamethasone suppression test than individuals diagnosed with clinical depression.[30][31]
In addition, most people with PTSD also show a low secretion of cortisol and high secretion of catecholamines in urine,with a norepinephrine/cortisol ratio consequently higher than comparable non-diagnosed individuals.This is in contrast to the normative fight-or-flight response, in which both catecholamine and cortisol levels are elevated after exposure to a stressor.
Brain catecholamine levels are high, and corticotropin-releasing factor (CRF) concentrations are high. Together, these findings suggest abnormality in the hypothalamic-pituitary-adrenal (HPA) axis.
The HPA axis is responsible for coordinating the hormonal response to stress. Given the strong cortisol suppression to dexamethasone in PTSD, HPA axis abnormalities are likely predicated on strong negative feedback inhibition of cortisol, itself likely due to an increased sensitivity of glucocorticoid receptors. Some researchers have associated the response to stress in PTSD with long-term exposure to high levels of norepinephrine and low levels of cortisol, a pattern associated with improved learning in animals.[citation needed]
Translating this reaction to human conditions gives a pathophysiological explanation for PTSD by a maladaptive learning pathway to fear response through a hypersensitive, hyperreactive, and hyperresponsive HPA axis.
Low cortisol levels may predispose individuals to PTSD: Following war trauma, Swedish soldiers serving in Bosnia and Herzegovina with low pre-service salivary cortisol levels had a higher risk of reacting with PTSD symptoms, following war trauma, than soldiers with normal pre-service levels.Because cortisol is normally important in restoring homeostasis after the stress response, it is thought that trauma survivors with low cortisol experience a poorly contained—that is, longer and more distressing—response, setting the stage for PTSD.
Other studies indicate that people who suffer from PTSD have chronically low levels of serotonin which contributes to the commonly associated behavioral symptoms such as anxiety, ruminations, irritability, aggression, suicidal, and impulsivity. Serotonin also contributes to the stabilization of glucocorticoid production.
Dopamine levels in patients with PTSD can help contribute to the symptoms associated. Low levels of dopamine can contribute to anhedonia, apathy, impaired attention, and motor deficits. Increased levels of dopamine can cause psychosis, agitation, and restlessness.
Hyperresponsiveness in the norepinephrine system can be caused by continued exposure to high stress. Overactivation of norepinephrine receptors in the prefrontal cortex can be connected to the flashbacks and nightmares frequently experienced by those with PTSD. A decrease in other norepinephrine functions (awareness of the current environment) prevents the memory mechanisms in the brain from processing that the experience, and emotions the person is experiencing during a flashback are not associated with the current environment.
However, there is considerable controversy within the medical community regarding the neurobiology of PTSD. A review of existing studies on this subject showed no clear relationship between cortisol levels and PTSD. However the majority of reports indicate people with PTSD have elevated levels of corticotropin-releasing hormone, lower basal cortisol levels, and enhanced negative feedback suppression of the HPA axis by dexamethasone
Neuroanatomy
Regions of the brain associated with stress and posttraumatic stress disorder
Three areas of the brain whose function may be altered in PTSD have been identified: the prefrontal cortex, amygdala, and hippocampus. Much of this research has utilised PTSD victims from the Vietnam War. For example, a prospective study using the Vietnam Head Injury Study showed that damage to the prefrontal cortex may actually be protective against later development of PTSD. In a study by Gurvits et al., combat veterans of the Vietnam War with PTSD showed a 20% reduction in the volume of their hippocampus compared with veterans who suffered no such symptoms.This finding could not be replicated in chronic PTSD patients traumatized at an air show plane crash in 1988 (Ramstein, Germany).
In human studies, the amygdala has been shown to be strongly involved in the formation of emotional memories, especially fear-related memories. Neuroimaging studies in humans have revealed both morphological and functional aspects of PTSD. However during high stress times the hippocampus, which is associated with the ability to place memories in the correct context of space and time, and with the ability to recall the memory, is suppressed. This suppression is hypothesized to be the cause of the flashbacks that often plague PTSD patients. When someone with PTSD undergoes a stimuli similar to the traumatic event the body perceives the event as occurring again because the memory was never properly recorded in the patients memory.
The amygdalocentric model of PTSD proposes that it is associated with hyperarousal of the amygdala and insufficient top-down control by the medial prefrontal cortex and the hippocampus particularly during extinction. This is consistent with an interpretation of PTSD as a syndrome of deficient extinction ability. A study at the European Neuroscience Institute-Goettingen (Germany) found that fear extinction-induced IGF2/IGFBP7 signalling promotes the survival of 17–19-day-old newborn hippocampal neurons. This suggests that therapeutic strategies that enhance IGF2 signalling and adult neurogenesis might be suitable to treat diseases linked to excessive fear memory such as PTSD. Further animal and clinical research into the amygdala and fear conditioning may suggest additional treatments for the condition.
The maintenance of the fear involved with PTSD has been shown to include the HPA axis, the locus coeruleus-noradrenergic systems, and the connections between the limbic system and frontal cortex. The HPA axis which coordinates the hormonal response to stresswhich activates the LC-noradrenergic system is implicated in the over consolidation of memories that occurs in the aftermath of trauma. This over consolidation increases the likelihood of developing PTSD. The amygdala is responsible for threat detection and the conditioned and unconditioned fear responses that are carried out as a response to a threat. The medial prefrontal cortex, part of the amygdala, can inhibit the conditioned fear responses during trauma.
The LC-noradrenergic system has been hypothesized to mediate the over-consolidation of fear memory in PTSD. High levels of cortisol reduces noradrenergic activity it is proposed that individuals with PTSD fail to regulate the increased noradrenergic response to traumatic stress. It is thought that the intrusive memories and conditioned fear responses to associated triggers is a result of this response. Neuropeptide Y has been reported to reduce the release of norepinephrine and has been demonstrated to have anxiolytic properties in animal models. Studies have shown people with PTSD demonstrate reduced levels of NPY, possibly indicating their increased anxiety levels.
The basolateral nucleus (BLA) of the amygdala is responsible for the comparison and development of associations between unconditioned and conditioned responses to stimuli which results in the fear conditioning present in PTSD. The BLA activates the central nucleus (CeA) which elaborates the fear response, (including behavioral response to threat and elevated startle response). Descending inhibitory inputs form the medial prefrontal cortex (mPFC) regulates the transmission from the BLA to the CeA which is hypothesized to play a role in the extinction of conditioned fear responses.
Genetics
There is evidence that susceptibility to PTSD is hereditary. Approximately 30% of the variance in PTSD is caused from genetics alone. For twin pairs exposed to combat in Vietnam, having a monozygotic (identical) twin with PTSD was associated with an increased risk of the co-twin having PTSD compared to twins that were dizygotic (non-identical twins).There is also evidence that those with a genetically smaller hippocampus are more likely to develop PTSD following a traumatic event. Research has also found that PTSD shares many genetic influences common to other psychiatric disorders. Panic and generalized anxiety disorders and PTSD share 60% of the same genetic variance. Alcohol, nicotine, and drug dependence shares greater than 40% genetic similarities.
Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain. A recent study reported significant interactions between three polymorphisms in the GABA alpha-2 receptor gene and the severity of childhood trauma in predicting PTSD in adults. A study found those with a specific genotype for G-protein signaling 2 (RGS2), a protein that decreases G protein-coupled receptor signaling, and high environmental stress exposure as adults and a diagnosis of lifetime PTSD. This was particularly prevalent in adults with prior trauma exposure and low social support.
Recently, it has been found that several single-nucleotide polymorphisms (SNPs) in FK506 binding protein 5 (FKBP5) interact with childhood trauma to predict severity of adult PTSD. These findings suggest that individuals with these SNPs who are abused as children are more susceptible to PTSD as adults.
This is particularly interesting given that FKBP5 SNPs have previously been associated with peritraumatic dissociation (that is, dissociation at the time of the trauma), which has itself been shown to be predictive of PTSD. Furthermore, FKBP5 may be less expressed in those with current PTSD.Another recent study found a single SNP in a putative estrogen response element on ADCYAP1R1 (encodes pituitary adenylate cyclase-activating polypeptide type I receptor or PAC1) to predict PTSD diagnosis and symptoms in females.Incidentally, this SNP is also associated with fear discrimination. The study suggests that perturbations in the PACAP-PAC1 pathway are involved in abnormal stress responses underlying PTSD.
PTSD is a psychiatric disorder which requires an environmental event which individuals may have varied responses to so gene-environment studies tend to be the most indicative of their effect on the probability of PTSD than studies of the main effect of the gene. Recent studies have demonstrated the interaction between PFBP5 and childhood environment to predict the severity of PTSD. Polymorphisms in FKBP5 have been associated with peritraumatic dissociation in mentally ill children. A study of highly traumatized African-American subjects from inner city primary care clinics indicated 4 polymorphisms of the FKBP5 gene, each of these were functional. The interaction between the polymorphisms and the severity of childhood abuse predicts the severity of the adult PTSD symptoms. A more recent study of the African-American population indicated that the TT genotype of the FKBP5 gene was associated with the highest risk of PTSD among those who experienced childhood adversity, however those with this genotype that experienced no childhood adversity had the lowest risk of PTSD. In addition alcohol dependence interacts with the FKBP5 polymorphisms and childhood adversity to increase the risk of PTSD in these populations. Emergency room expression of the FKPB5 mRNA following trauma was shown to indicate a later development of PTSD.
Catechol-O-methyl transferase (COMT) is an enzyme that catalyzes the extraneuronal breakdown of catecholamines. The gene that codes for COMT has a functional polymorphism in which a valine has been replaced with a methionine at condon 158. This polymorphism has lower enzyme activity and has been tied to slower breakdown of the catecholamines. A study, of Rwandan Genocide survivors, indicated that carriers of the Val allel demonstrated the expected response relationship between the higher number of lifetime traumatic events and a lifetime diagnosis of PTSD. However those who were homozygotes for the Met/Met genotype demonstrated a high risk of lifetime PTSD independent of the number of traumatic experiences. Those with Met/Met genotype also demonstrated a reduced extinction of conditioned fear responses with may account for the high risk for PTSD experienced by this genotype.
Many genes impact the limbic-frontal neurocircuitry as a result of its complexity. The main effect of the D2A1 allele of the dopamine receptor D2 (DRD2) has a strong association with the diagnosis of PTSD. The D2A1 allele has also shown a significant association to PTSD in those who engaged in harmful drinking. In addition a polymorphism in the dopamine transporter SLC6A3 gene has a significant association with chronic PTSD. A polymorphism of the serotonin receptor 2A gene has been associated with PTSD in Korean women. The short allele of the promoter region of the serotonin transporter (5-HTTLPR) has been shown to be less efficient than the long allele and is associated with the amygdala response for extinction of fear conditioning. However the short allele is associated with a decreased risk of PTSD in a low risk environment but a high risk of PTSD in a high risk environment. The s/s genotype demonstrated a high risk for development of PTSD even in response to a small number of traumatic events but those with the l allele demonstrate increasing rates of PTSD with increasing traumatic experiences.
Genome-wide association study (GWAS) offer an opportunity to identify novel risk variants for PTSD which will in turn inform our understanding of the etiology of the disorder. Early results indicate the feasibility and potential power of GWAS to identify biomarkers for anxiety-related behaviors that suggest a future of PTSD. These studies will lead to the discovery of novel loci for the susceptibility and symptomatology of anxiety disorders including PTSD.
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Epigenetics
Gene and environment studies alone fail to explain the importance the developmental stressors timing exposure to the phenotypic changes associated with PTSD. Epigenetic modification is the environmentally induced change in DNA which alters the function rather than the structure of the gene. The biological mechanism of epigenetic modification typically involves the methylation of cytosine within a gene which produces decreased transcription of that segment of DNA. The neuroendocrine alteration seen in animal models parallel those of PTSD in which low basal cortisol and enhanced suppression of cortisol in response to synthetic glucocorticoid becomes hereditary. Lower levels of glucocorticoid receptor (GR) mRNA have been demonstrated in the hippocampus of suicide victims with histories of childhood abuse. It hasn’t been possible to monitor the state of methylation over time however the interpretation is early developmental methylation changes are long-lasting and enduring. It is hypothesized that epigenetic-mediated changes in the HPA axis could be associated with an increased vulnerability to PTSD following traumatic events. These findings support the mechanism in which early life trauma strongly validates as a risk factor for PTSD development in adulthood by recalibrating the set point and stress-responsiveness of the HPA axis. Studies have reported an increased risk for PTSD and low cortisol levels in the offspring of female holocaust survivors with PTSD. Epigenetic mechanisms may also be relevant to the intrauterine environment. Mothers with PTSD produced infants with lower salivary cortisol levels only if the traumatic exposure occurred during the third trimester of gestation. These changes occur via transmission of hormonal responses to the fetus leading to a reprogramming of the glucocorticoid responsivity in the offspring.[38]
Risk factors
See also: Psychological resilience
Although most people (50–90%) encounter trauma over a lifetime, about 20-30% develop PTSD but over half of these people will recover without treatment. Vulnerability to PTSD presumably stems from an interaction of biological diathesis, early childhood developmental experiences, and trauma severity. A person that never established secure relationships and learned coping skills as a young child if exposed to a traumatic experience is more likely to develop PTSD than one that developed good coping skills and has a support network.
Predictor models have consistently found that childhood trauma, chronic adversity, and familial stressors increase risk for PTSD as well as risk for biological markers of risk for PTSD after a traumatic event in adulthood.Peri-traumatic dissociation in children is a predictive indicator of the development of PTSD later in life. This effect of childhood trauma, which is not well understood, may be a marker for both traumatic experiences and attachment problems. Proximity to, duration of, and severity of the trauma also make an impact, and interpersonal traumas cause more problems than impersonal ones.
Military experience
Schnurr, Lunney, and Senguptaidentified risk factors for the development of PTSD in Vietnam veterans. Among those are:
- Hispanic ethnicity, coming from an unstable family, being punished severely during childhood, childhood asocial behavior, and depression as pre-military factors
- War-zone exposure, peritraumatic dissociation, depression as military factors
- Recent stressful life events, post-Vietnam trauma, and depression as post-military factors
They also identified certain protective factors, such as:
- Japanese-American ethnicity, high school degree or college education, older age at entry to war, higher socioeconomic status, and a more positive paternal relationship as pre-military protective factors.
- Social support at homecoming and current social support as post-military factors.Other research also indicates the protective effects of social support in averting PTSD or facilitating recovery if it develops.
Glass and Jones found early intervention to be a critical preventive measure:
“PTSD symptoms can follow any serious psychological trauma, such as exposure to combat, accidents, torture, disasters, criminal assault and exposure to atrocities or to the sequelae of such extraordinary events. Prisoners of war exposed to harsh treatment are particularly prone to develop PTSD. In their acute presentation these symptoms, which include subsets of a large variety of affective, cognitive, perceptions, emotional and behavioral responses which are relatively normal responses to gross psychological trauma. If persistent, however, they develop a life of their own and may be maintained by inadvertent reinforcement. Early intervention and later avoidance of positive reinforcement (which may be subtle) for such symptoms is a critical preventive measure.
Studies have shown that those prepared for the potential of a traumatic experience are more prepared to deal with the stress of a traumatic experience and therefore less likely to develop PTSD.
Foster care
In the Casey Family Northwest Alumni Study, conducted in conjunction with researchers from the Harvard Medical School in Oregon and Washington state, the rate of PTSD in adults who were in foster care for one year between the ages of 14–18 was found to be higher than that of combat veterans. Up to 25% of those in the study meet the diagnostic criteria for PTSD as compared to 12–13% of Iraq war veterans and 15% of Vietnam War veterans, and a rate of 4% in the general population. The recovery rate for foster home alumni was 28.2% as opposed to 47% in the general population.
Dubner and Motta (1999)found that 60% of children in foster care who had experienced sexual abuse had PTSD, and 42% of those who had been physically abused met the PTSD criteria. PTSD was also found in 18% of the children who were not abused. These children may have developed PTSD due to witnessing violence in the home, or as a result of real or perceived parental abandonment.
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