Functional somatic syndrome (FSS) (sometimes termed "non-specific physical disorders") refers to a cluster of chronic conditions, characterized by persistent physical symptoms without demonstrable structural or organic disease despite extensive medical testing.[9]
Fibromyalgia, chronic fatigue syndrome (now called ME/CFS) and irritable bowel syndrome and are some of the most common disorders that have been described as FSS conditions,[14][15][16] although the classification of ME/CFS as an FSS has been increasingly called into question in the recent years.[17][18][19] Functional somatic syndromes are very common, although specific criteria differ, they are estimated to affect about anywhere from 4% to 16% of the general population.[20][21][22][23]
Definition and Terminology
FSS refers to disturbances in bodily functioning where aetiology is unknown.[24] The term ‘functional somatic disorders’ (FSD) was proposed in 2020.[25]
Related terms
"Medically unexplained physical symptoms" only include symptoms where no explanation is found at all, but not poorly understood syndromes like fibromyalgia or IBS. These symptoms can sometimes be worsened in the presence of mental health problems.[26]
"Persistent physical symptoms"[27] 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.
Classification
Being an umbrella term, the disorder is not encoded in the ICD-11, rather its separate manifestations have specific codes there. Proposals for classifications have been made.[28]
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[29][30] or into one general functional somatic disorder given the finding of correlations between symptoms and underlying etiologies.[31]
FSS conditions
The following conditions are often considered to be representations of the functional somatic syndrome:
A considerable overlap of symptoms exists between the FSS diagnoses, with high rates of comorbidity between them. For example, the prevalence of comorbid FSS diagnoses ranges from 20% to 70%, while comorbid affective disorders with a fibromyalgia diagnosis ranges from 20% to 80%.[39]
Prevalence
Studies have found prevalence in the general population of having at least one FSS of 16.3% (n = 9656),[40] and 9.3% (n = 3054).[41]
Some 10% of the general population, and around 33% of adult patients in clinical populations, suffer from functional somatic symptoms.[42]
Potential causes
A mixture of physical and psychological factors may predict FSS.[9][28]
Psychological factors
Low-quality evidence suggests that patients with somatic syndromes, such as fibromyalgia and irritable bowel syndrome, tend to have a more frequent history of both physical and sexual abuse prior to the onset of their physiological symptoms. Additionally, patients show higher rates of previous emotional abuse, emotional neglect, and physical neglect when compared to the general population.[43]
Attentional bias has been posited as the psychological mechanism by which trauma and somatic symptoms are tied.[44][45][unreliable medical source?] Attentional bias refers to the idea that traumatic events can cause individuals to become more attuned to their bodily functions, thus intensifying the perception of pain, fatigue, and other common somatic symptoms.[45][unreliable medical source?] 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 health anxiety, wherein the patient becomes increasingly concerned that common somatic symptoms are related to a physical disease or injury, and therefore, another potential bodily threat.[44][unreliable medical source?] An initial perception of lost control can further intensify 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.[46][unreliable medical source?] 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, physiological symptoms, such as heart palpitations, dizziness, and breathlessness.[47][unreliable medical source?]
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.[48] When an individual experiences a traumatic event, the HPA axis causes the increased release of cortisol, activating the sympathetic nervous system and causing negative feedback to be sent to the hypothalamus and pituitary gland. In people who have experienced major trauma, this reaction can become dysfunctional and can cause a chronic decrease in cortisol production, though the rates of this decrease in cortisol levels vary across different types and frequencies of trauma.[49]
Diagnosis
Diagnosis of a FSS is usually a diagnosis of exclusion, where physicians rule out other disorders that could explain the dysfunctions being experienced.[50] The DDx is often complex and involves factual organic pathology, as well as a number of psychiatric disorders, including somatic delusions, primary mood/anxiety disorders with somatic manifestations, somatic symptom disorder, illness anxiety disorder, functional neurological disorder, factitious disorder, and malingering, as well as primary deconditioning.
Management and Treatment
Psychological interventions are considered the primary treatment for functional somatic syndromes, with cognitive behavioral therapy (CBT) representing the most empirically supported approach. Systematic reviews indicate CBT reduces somatic symptom severity and disability through small-to-moderate effect sizes, primarily by modifying maladaptive illness beliefs and reducing avoidance behaviors rather than altering symptom intensity directly. Short-term psychodynamic psychotherapy (STPP) has demonstrated efficacy comparable or superior to CBT in long-term follow-up studies, while third-wave therapies such as mindfulness-based interventions and Acceptance and Commitment Therapy (ACT) target psychological flexibility and experiential avoidance. Psychoeducation regarding the psychophysiological mechanisms of symptoms serves as a foundational component across all modalities, aiming to reframe the patient's understanding of their condition from organic disease to functional dysregulation.[51][52][53][54]
Physical therapies for functional somatic syndromes primarily comprise graded exercise therapy, structured aerobic training, and activity-based rehabilitation programs that aim to reverse deconditioning and reduce symptom-focused inactivity. Graded exercise therapy typically involves individually titrated, stepwise increases in physical activity (e.g., walking, cycling) under supervision, with progression guided by time rather than symptoms to prevent reinforcement of avoidance behavior. Additional components include physiotherapy targeting posture, muscle tension, and pain-modulating movement patterns, as well as occupational therapy interventions that systematically rebuild daily functioning and participation in work and leisure activities. These interventions are predicated on evidence that functional symptoms are maintained by a cycle of inactivity, hypervigilance to bodily sensations, and fear-avoidance, and they therefore emphasize behavioral activation and exposure to normal levels of exertion rather than passive modalities such as rest or purely palliative treatments.[55][56]
Medications such as antidepressants may play a role.[57][58] More direct medication has little if any positive long-term impact.[9]
According to guidance from the German Federal Ministry of Health "the extent to which functional somatic syndromes affect people’s lives partly depends on how the people affected deal with them."[9]
History
The term functional somatic syndrome was used in a 1999 paper.[59]
↑Bourke JH, Langford RM, White PD (March 2015). "The common link between functional somatic syndromes may be central sensitisation". Journal of Psychosomatic Research. 78 (3): 228–236. doi:10.1016/j.jpsychores.2015.01.003. ISSN1879-1360. PMID25598410.
↑Petersen MW, Schröder A, Jørgensen T, Ørnbøl E, Dantoft TM, Eliasen M, etal. (July 2020). "Prevalence of functional somatic syndromes and bodily distress syndrome in the Danish population: the DanFunD study". Scandinavian Journal of Public Health. 48 (5): 567–576. doi:10.1177/1403494819868592. ISSN1651-1905. PMID31409218.
123456789"2.2 The Putative Disappearance of Somatic Manifestations of Hysteria", From Photography to fMRI, transcript Verlag, pp.219–237, 2022-12-31, doi:10.1515/9783839461761-009, ISBN978-3-8394-6176-1, In the late 1990s, it became a matter of heated debate if hysteria's nosological successors were conceptually and diagnostically distinguishable from a range of possibly related clinical conditions that were equally characterised by the lack of any demonstrable physical abnormality. Jointly referred to as functional somatic syndromes, these conditions include multiple chemical sensitivity, sick building syndrome, chronic fatigue syndrome, fibromyalgia, irritable bowel syndrome, chronic whiplash, chronic Lyme disease, the Gulf War syndrome, food allergies, hypoglycaemia. To this date, the delineation between present-day forms of hysteria and other functional somatic syndromes remains unresolved.{{citation}}: CS1 maint: work parameter with ISBN (link)
↑Petersen MW, Schröder A, Jørgensen T, Ørnbøl E, Dantoft TM, Eliasen M, etal. (July 1, 2020). "Prevalence of functional somatic syndromes and bodily distress syndrome in the Danish population: the DanFunD study". Scandinavian Journal of Public Health. 48 (5): 567–576. doi:10.1177/1403494819868592. PMID31409218.
↑Fischer S, Gaab J, Ehlert U, Nater UM (June 1, 2013). "Prevalence, overlap, and predictors of functional somatic syndromes in a student sample". International Journal of Behavioral Medicine. 20 (2): 184–193. doi:10.1007/s12529-012-9266-x. PMID23055025.
↑Yavne Y, Amital D, Watad A, Tiosano S, Amital H (August 2018). "A systematic review of precipitating physical and psychological traumatic events in the development of fibromyalgia". Seminars in Arthritis and Rheumatism. 48 (1): 121–133. doi:10.1016/j.semarthrit.2017.12.011. PMID29428291. S2CID205143853.
12Golding JM (March 1994). "Sexual assault history and physical health in randomly selected Los Angeles women". Health Psychology. 13 (2): 130–138. doi:10.1037/0278-6133.13.2.130. PMID8020456.
↑Antony MM, Brown TA, Craske MG, Barlow DH, Mitchell WB, Meadows EA (September 1995). "Accuracy of heartbeat perception in panic disorder, social phobia, and nonanxious subjects". Journal of Anxiety Disorders. 9 (5): 355–371. doi:10.1016/0887-6185(95)00017-i. ISSN0887-6185.
↑Bryant RA (2011-07-15). "Psychological Interventions for Trauma Exposure and PTSD". Post-Traumatic Stress Disorder. John Wiley & Sons, Ltd. pp.171–202. doi:10.1002/9781119998471.ch5. ISBN9781119998471.
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