Functional somatic syndrome

One commonly cited hypothesis in the literature implicates the hypothalamic–pituitary–adrenal axis (HPA axis) and cortisol secretion in the manifestation of somatic symptoms following trauma.[9] The HPA axis plays a major role in moderating the body's stress response to both emotional and physical pain, relating to both the experience of psychological symptoms prevalent following trauma as well as the physiological symptoms prevalent in FSS conditions.[10] When an individual experiences a traumatic event, the HPA-axis causes the increased release of cortisol, activating the sympathetic nervous pathway and causing negative feedback to be sent to the hypothalamus and pituitary gland. In people who have experienced significant trauma, this reaction can become dysfunctional and can cause a chronic decrease in cortisol production, though the rates of this decrease in cortisol levels varies across different types and frequencies of trauma.[11] For example, fibromyalgia is characterized as a stress response disorder; similar to trauma, patients with fibromyalgia demonstrate a susceptibility to neuroendocrine dysfunctions. Fibromyalgia patients statistically exhibit atypical patterns of daily cortisol secretion, as well as significantly low urine cortisol levels.[9]

Patients with somatic syndromes such as fibromyalgia and irritable bowel syndrome have significantly higher rates of both physical and sexual abuse prior to the onset of their physiological symptoms, as well as higher rates of previous emotional abuse, emotional neglect, and physical neglect compared to the general population.[12] Further, childhood trauma such as sexual abuse or maltreatment can indicate an increased propensity for later somatic syndrome onset. Current theories propose an "attentional bias" as the psychological mechanism by which trauma and somatic symptoms are tied.[13][14] The concept of attentional bias refers to the idea that traumatic events can cause individuals to become more attuned to their bodies, thus intensifying the perception of pain, fatigue, and other common somatic symptoms.[14] The initial traumatic event is interpreted as a threat to the body, and therefore the stress-response of the body takes on a new, heightened awareness to any potential subsequent threats. This attentional bias leads to a "health anxiety," where the patient becomes increasingly concerned that common somatic symptoms are related to a physical disease or injury, and therefore, another potential bodily threat.[13] An initial perception of lost control can further lead to this attentional bias; sense of control is negatively associated with symptom reporting, suggesting that somatic symptoms are more closely monitored when psychologically recovering from an incident of lost control.[15] Functional Somatic Syndromes are thought to be a result of conditioned hyperarousal following a trauma; victims are conditioned to respond more sensitively to the somatic symptoms following a trauma by their attention to and reinforcement of the symptom existence. This feedback loop is similar to that of panic disorder, in which fear of a subsequent panic attack causes an increased hyper-vigilance towards, and exacerbation of, certain physiological symptoms, such as heart palpitations, dizziness, and breathlessness.[16]