What clinical features can help differentiate Functional Neurological Disorder from other neurological conditions?

Functional Neurological Disorder (FND) can be differentiated from other neurological conditions by several key clinical features:

• Symptom variability and inconsistency: FND symptoms such as limb or facial weakness often fluctuate and may evolve over time, frequently increasing during periods of stress, unlike typical progressive neurological diseases where symptoms tend to follow a consistent pattern NICE NG127.
• Absence of new neurological signs in known FND cases: Adults diagnosed with FND by a specialist may have recurrent symptoms like limb weakness without new neurological signs, which suggests a functional rather than structural cause NICE NG127.
• Discrepancy between reported symptoms and neurological examination: In FND, clinical signs may not correspond to known neuroanatomical pathways, for example, weakness that does not follow a nerve or root distribution, or positive signs such as Hoover’s sign (incongruent weakness) NICE NG127.
• Normal neuroimaging and electrophysiological studies: Unlike many organic neurological disorders, FND typically lacks objective abnormalities on imaging or nerve conduction studies, supporting a diagnosis based on clinical features NICE NG127.
• Associated cognitive and concentration difficulties: Memory and concentration problems can be part of FND and anxiety disorders, but these do not usually indicate progressive neurological disease if no new neurological signs are present NICE NG127; Cabreira et al. 2023.
• Rapid onset and fluctuating course: FND symptoms often have a sudden onset and may fluctuate markedly, contrasting with the usually progressive or stable course of many neurological diseases NICE NG127.
• Positive clinical signs specific to FND: Certain clinical tests (e.g., inconsistency on repeated examination, distractibility of symptoms) help differentiate FND from organic neurological conditions NICE NG127.

In summary, the diagnosis of FND relies heavily on identifying clinical features such as symptom variability, inconsistency with known neurological patterns, absence of objective neurological deficits, and the presence of cognitive symptoms without progressive neurological signs. These features help distinguish FND from other neurological disorders that typically show consistent, progressive, and anatomically congruent signs and objective abnormalities on investigations NICE NG127; Cabreira et al. 2023.