What they say about fatigue and 'fatigue syndromes' in the paper.
"Somatic and pain-related comorbidities were discussed in 11 of the reviewed studies, focusing on chronic pain, fibromyalgia, fatigue syndromes, gastrointestinal disturbances, and functional sensory symptoms."
"Somatic and Pain Comorbidities
Somatic symptoms and chronic pain are central to the PNES and FMD comorbidity spectrum. Chronic pain, fibromyalgia, fatigue syndromes, and gastrointestinal disturbances are commonly reported in PNES, sometimes overshadowing seizure-like episodes and leading to diagnostic confusion [94]. FMD also demonstrates significant overlap with pain syndromes, including functional pain disorders and fatigue, particularly in patients with coexisting gait disturbances and dystonia."
"In the case of Functional Cognitive Disorder (FCD), psychiatric conditions, particularly anxiety disorders, depression, and health-related anxiety, frequently dominate the clinical picture. Our findings reveal that anxiety was present in over 48% of FCD cases, with depression and fatigue following closely. These comorbidities do not merely coexist with cognitive complaints but are deeply intertwined with the phenomenology of the disorder."
"Functional Movement Disorder (FMD) emerged in this study as the subtype most consistently associated with a high overall burden of comorbidities. Psychiatric comorbidities were strikingly prevalent, with depression present in over 70% of cases and anxiety exceeding 80% in several datasets. Early life trauma and adverse childhood experiences were also frequently reported, suggesting a significant role for stress and psychological vulnerability in shaping motor symptomatology [
8]. Fatigue, chronic pain, and migraine were among the most common physical comorbidities."
"The presence of these symptoms may also impair engagement with rehabilitation, particularly when pain and fatigue reduce physical stamina or increase activity avoidance. Therefore, these findings underscore the importance of a personalized, interdisciplinary model of care that incorporates pain management, physiotherapy, psychological support, and trauma-informed intervention"
"Across all FND subtypes, our cluster and correlation analyses revealed frequent co-occurrence of specific comorbidities, such as the pairing of anxiety and depression, or fatigue and chronic pain [
113,
114]. These combinations often form distinct clinical phenotypes that transcend traditional subtype boundaries. Such comorbidity patterns have substantial implications for both diagnosis and treatment. Patients with high comorbidity burdens tend to experience longer symptom duration, increased functional impairment, and reduced responsiveness to single-modality interventions. Furthermore, comorbid conditions often shape how patients interpret their symptoms. For instance, individuals with fibromyalgia or chronic fatigue may interpret new neurological symptoms as further evidence of an organic or degenerative illness, thereby reinforce maladaptive illness beliefs and increasing resistance to the functional formulation."
"Clinicians must also remain vigilant for the risk of diagnostic overshadowing, where attention to comorbid psychiatric symptoms may lead to under-recognition of the functional neurological presentation, or conversely, where functional symptoms obscure serious coexisting medical conditions"
"In conclusion, functional neurological disorder (FND) reveals its complexity only when viewed through a biopsychosocial prism: biological predisposition, traumatic events and social context intertwine to generate a diverse range of clinical manifestations. Psychiatric comorbidities such as anxiety, depression and PTSD, as well as somatic comorbidities, chronic pain, fatigue or sleep disorders, are not simple coincidences, but active partners in the maintenance of functional symptoms. This subtle interaction explains why in psychogenic non-epileptic epilepsy, the burden of trauma often precedes seizures, why in functional motor disorders feelings of pain and exhaustion make the rehabilitation process difficult and why in functional cognitive disorders, cognitive anxiety amplifies the feeling of “mental fog” and the avoidance of challenging situations.
Across all subtypes, the high prevalence of psychiatric and somatic comorbidities is a defining feature of FND, with direct implications for prognosis and therapeutic planning. Their systematic identification should be considered a priority in both research and routine clinical practice, as failure to address them adequately can limit treatment response and increase the risk of relapse.
Early, comprehensive, and multidimensional assessment thus becomes the cornerstone of any therapeutic plan: a careful trauma history, specific dissociation and quantification scales for pain, fatigue, and sleep disorders, as well as detailed neuropsychological assessment can quickly identify vulnerable areas and direct the patient to the most appropriate services. In the absence of this early triage, the diagnosis risks remaining fragmented, and the patient caught between specialties, may be left without a clear path to recovery.
In practice, treatment must adapt to each comorbidity profile: from trauma-focused therapies, such as trauma-focused CBT or EMDR, for people with histories marked by adverse events, to multidisciplinary rehabilitation programs that combine graded exercises and cognitive strategies for pain and fatigue management, and to metacognitive interventions and attention and memory training exercises for those affected by functional cognitive disorders. In all these situations, validating symptoms and establishing common goals strengthen the therapeutic alliance and increase adherence to treatment."
