Functional somatic syndrome

Functional somatic syndrome (FSS) is a syndrome in which any of a group of chronic symptoms occur with no identifiable organic cause. Fibromyalgia is the leading FSS condition, among many. FSS conditions are highly prevalent, but little is known about their etiology.

Functional somatic syndrome
Specialty	Psychiatry

Biological markers for the FSS diagnoses are non-existent, making the categorization difficult. Diagnosis is by exclusion.

Definition and Terminology

FSS refers to disturbances in bodily functioning where aetiology is unknown,^[1] including that psychogenesis is not assumed.^[2]

Related terms

"Medically unexplained physical symptoms" include FSS situations, but also situations where the symptoms are sporadic and where psychogenesis may be suspected.^[3]

"Persistent physical symptoms"^[4] includes FSS situations but also situations where persistent physical symptoms are caused by a known illness, such as arthritis.

In somatic symptom disorder chronic physical symptoms, which may or may not be linked to a known illness, coincide with excessive and maladaptive thoughts, emotions, and behaviors connected to those symptoms. In FSS these features are not present.

Signs and symptoms

Functional somatic syndromes are characterized by ambiguous, non-specific symptoms that appear in otherwise-healthy people. Overlap in symptomology exists across diagnoses, including gastrointestinal issues, pain, fatigue, cognitive difficulties, and sleep difficulties. Some have proposed to group symptoms into clusters^[5][6] or into one general functional somatic disorder given the finding of correlations between symptoms and underlying etiologies.^[7][8]

Pre-diagnosis contact with health systems

A large (n = 43,676) 2020 study found that 5 years prior to diagnosis, FSS patients consulted more frequently for a range of psychological and somatic conditions than did controls. Around half this cohort were ME/CFS patients (normally not termed an FSS).^[9]

FSS conditions

FSS disorders include

• fibromyalgia (FM),^[10]
• temporomandibular disorder,
• irritable bowel syndrome,^[10][11]
• lower back pain,
• tension headache,
• atypical face pain,
• non-cardiac chest pain,
• insomnia,
• palpitation,
• dyspepsia,
• dizziness.^[12]
• certain claims of food allergies^[10] (when no true allergy can be demonstrated)
• Gulf War syndrome^[10]
• certain claims of hypoglycaemia^[10] (symptoms appearing when the blood sugar is normal)
• Chronic Lyme disease^[10]
• Multiple chemical sensitivity^[10]
• Sick building syndrome^[10]
• Chronic whiplash^[10]

Overlap of FSS conditions

A large overlap of symptoms exist between the FSS diagnoses, causing high rates of comorbidity between them; the prevalence of comorbid FSS diagnoses ranges from 20% to 70%, while comorbid affective disorders with a fibromyalgia diagnosis ranges from 20% to 80%.^[13]

ME/CFS not an FSS

ME/CFS^[14] is classified by major health bodies such as the NAM, WHO, and NIH as an organic disease,^[15][16][17] and there are consistent findings of biological abnormalities, although the aetiology remains unclear.

Prevalence

Studies have found prevalence in the general population of having at least one FSS of 16.3% (n = 9656),^[18] and 9.3% (n = 3054).^[19]

Some 10% of the general population, and around 33% of adult patients in clinical populations, suffer from functional somatic symptoms.^[20]

Comorbidity

PTSD

Rates of PTSD are roughly 9.5–43.5% higher in people seeking treatment for a functional somatic syndrome as opposed to the general population.^[21]

Potential causes

Psychological factors

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.^[22] Further, childhood trauma such as sexual abuse or maltreatment can indicate an increased propensity for later somatic syndrome onset.

"Attentional bias" has been posited as the psychological mechanism by which trauma and somatic symptoms are tied.^[23][24] 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.^[24] 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.^[23] 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.^[25] 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.^[26]

Biological factors

One hypothesis implicates the hypothalamic–pituitary–adrenal axis (HPA axis) in the manifestation of somatic symptoms following trauma. 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.^[27] 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.^[28]

Diagnosis

Diagnosis of a FSS is usually a diagnosis of exclusion, where physicians rule out other disorders that could explain the dysfunctions being experienced.^[29]

Management and Treatment

CBT can be helpful for FSS. Medications such as antidepressants may play a role.^[30][31]

History

The term functional somatic syndrome was used in a 1999 paper.^[32]