Neurology
A diagnosis of functional neurological disorder can be made by an experienced neurologist based on positive clinical signs. Before making a diagnosis, it is important that the neurologist carries out a thorough examination, as well as all the necessary tests to help rule out other neurological disorders. It is useful to ask the patient about any symptoms present, focusing on the mechanisms of occurrence (looking for pathophysiological triggers such as migraine, acute pain, panic disorder, infection, adverse drug reactions, etc.).
It is also important to ask about secondary symptoms, which often impair the patient's quality of life and will also be a potential barrier to his/her recovery (e.g. sleep, fatigue, pain, concentration and residual cognitive symptoms).
Common diagnostic errors
Failure to take into account comorbidity with another medical condition
Functional neurological disorder is often comorbid with other neurological disorders. As many as 20% of patients with functional (dissociative) seizures are also diagnosed with epilepsy. FND may also represent the initial stage of Parkinson's disease, due to shared neurobiological mechanisms.
Reliance on unusual clinical signs
As with some neurological disorders, FND has unusual clinical features (e.g. the ability to self-induce seizures), but it is crucial that the diagnosis is not made on the basis of their presence alone! FND is diagnosed on the basis of positive clinical features (read more under the tab diagnosis. )
Diagnosis based solely on psychiatric comorbidities and/or recent stress
Although FND is considered to have a high comorbidity with psychiatric disorders (e.g. anxiety, depression, etc.), it is a mistake to make a diagnosis based solely on the assumption of a psychogenic cause. In many patients, the disorder is triggered by an injury, accident or surgery.
Some examples of communication with FND patients
(adapted from Bennett et al., 2021).
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Bennett, K., Diamond, C., Hoeritzauer, I., Gardiner, P., McWhirter, L., Carson, A., in Stone, J. (2021). A practical review of functional neurological disorder (FND) for the general physician. Clinical Medicine, 21(1), 28.
Herbert, L. D., Kim, R., Hassan, A. A., Wilkinson-Smith, A., in Waugh, J. L. (2021). When neurologists diagnose functional neurological disorder, why don't they code for it?. CNS Spectrums, 26(6), 664-674.
Perez, D. L., Hunt, A., Sharma, N., Flaherty, A., Caplan, D., in Schmahmann, J. D. (2020). Cautionary notes on diagnosing functional neurological disorder as a neurologist-in-training. Neurology: Clinical Practice, 10(6), 484-487.
Stone, J., Burton, C., in Carson, A. (2020). Recognising and explaining functional neurological disorder. bmj, 371.