What is functional neurological disorder?

Functional neurological disorder (FND) is a disabling condition which predominately affects young and middle-aged adults. FND is thought to affect how the brain sends and receives information, resulting in heterogenous clinical presentations impacting motor and sensory function. In addition to commonly reported symptoms such as abnormal movements and seizures, many patients with FND report pain and are diagnosed with pain-related conditions (Steinruecke et al., 2024).

How prevalent is pain in FND?

Chronic pain is highly prevalent in patients with FND. A recent systematic review and meta-analysis showed that approximately 55% of patients with FND report some form of pain (Steinruecke et al., 2024). Of which, 22% of patients experienced complex regional pain syndrome, 16% of patients suffered from irritable bowel syndrome and 10% of patients suffered from fibromyalgia. Patients with FND are more likely to report pain in both affected and unaffected limbs compared with individuals with other neurological conditions. These findings highlight how assessing pain can support clinical and medicolegal professionals to differentiate patients with epilepsy vs. seizure type FND. Since chronic pain is highly prevalent amongst patients with FND, this also raises the question whether this symptom should be featured within diagnostic classification systems.

How is pain experienced in FND?

Since the experience of pain can be distressing, pain is typically the primary complaint amongst patients with FND presenting to emergency services (Steinrueke et al., 2024). The high symptom burden and functional impact of chronic pain in the context of FND is highlighted by the fact that 86% of these patients will have a lifetime diagnosis of depression and 25% of these individuals will attempt suicide (Mason et al., 2023). These findings highlight the disease burden felt by patients with both FND and chronic pain, underscoring the critical need to ensure that these patients are accurately diagnosed and treated.

Is pain part of the disorder?

The presence of pain is not required for a diagnosis of FND. A diagnosis of FND can be made using the DSM-5 if the patient experiences one or more symptoms affecting body movement or the senses. Typical examples of symptoms affecting body movement include spasms or tics, and typical examples of symptoms affecting the senses include double vision, ringing in the ears, a lack of smell or a feeling of numbness. These symptoms should cause significant distress or lead to significant impairments in social or occupational functioning. Pain could be experienced by patients secondary to the effects of abnormal movements in FND, such as body spasms resulting in injury. However, reports that pain is commonly experienced by patients with FND and findings that pain often precedes the onset of other FND symptoms does raise the question whether the experience of pain is in fact part of the condition (Steinruecke et al., 2024). Further research is needed to investigate the etiology and pathophysiology of pain in the context of FND to address this.

How should pain in FND be treated?

Unfortunately, physiotherapy programmes to support the clinical management of chronic pain have been unable to modulate the incidence or the severity of pain in the context of FND even when other FND symptoms improve (Steinruecke et al., 2024). Instead, opiate analgesics are commonly prescribed to patients with chronic pain in the context of FND. However, these medications are associated with side effects and can lead to physical dependence and addiction. These findings highlight the unmet clinical need to support the clinical management of pain in patients with FND.

There is a high prevalence of psychiatric conditions amongst patients with FND and chronic pain, where 86% of these patients will have a lifetime diagnosis of depression and 25% of these individuals will attempt suicide (Mason et al., 2023). Given the high prevalence of psychiatric conditions in FND with chronic pain, the neurologist or primary care physician should ensure they screen for psychiatric disorders and make referrals to psychiatric services as appropriate to support the clinical management of co-morbid psychiatric conditions (Gilmour et al., 2020).

References

Gilmour, G. S., Nielsen, G., Teodoro, T., Yogarajah, M., Coebergh, J. A., Dilley, M. D., … & Edwards, M. J. (2020). Management of functional neurological disorder. Journal of Neurology, 267, 2164-2172.

Mason I, Renée J, Marples I, et al. Functional neurological disorder is common in patients attending chronic pain clinics. Eur J Neurol. 2023; 30: 2669-2674. doi:10.1111/ene.15892

Steinruecke M, Mason I, Keen M, et al
Pain and functional neurological disorder: a systematic review and meta-analysis
Journal of Neurology, Neurosurgery & Psychiatry 2024;95:874-885.