Functional Neurological Disorder (FND) is a neurological condition that affects how the brain and nervous system work. It occurs when brain networks controlling movement, sensation, speech, or awareness stop working properly, even though the structure of the brain is normal. FND is increasingly described as a “brain network disorder”. A diagnosis of FND is made by a neurologist, based on positive neurological signs that are specific to the condition, not by exclusion. For example, Hoover’s sign can help confirm functional limb weakness. These positive signs distinguish FND from other neurological disorders and support accurate diagnosis and treatment. NHS England and NICE (NG252, 2025) recognise FND as a neurological disorder of function, reflected in clinical pathways and national service specifications that place FND alongside other neurological conditions within specialised neurology services. Symptoms can include limb weakness or paralysis, functional seizures, walking difficulties, spasms, sensory changes, speech or cognitive problems, and more.

What does functional mean?

In medicine, functional describes a problem in how a part of the body works, rather than damage to its structure. As noted by the Oxford Learner’s Dictionary, a functional disorder is “an illness caused when an organ of the body fails to perform its function”. In FND, this means the nervous system’s function is disrupted. Signals can be misrouted or inhibited, affecting the brain’s control of the body. Modern research using brain imaging and neurophysiological studies shows measurable changes in these networks. FND is therefore understood as a disorder of nervous system function, not a diagnosis of exclusion and not explained by stress or emotion alone.

How FND differs from other neurological conditions

FND can resemble conditions such as Multiple Sclerosis, Parkinson’s disease, or Epilepsy, but the underlying mechanism is different. Those conditions involve structural damage or disease in the nervous system, whereas FND involves abnormal function within normal structure. Both are neurological – they simply differ in how the brain and nervous system are affected.

“Functional Neurological Disorder is often explained to patients as a psychological reaction due to past trauma, or as symptoms due to stress. These explanations often fail, leaving patients feeling alienated, stigmatised, and not believed. The reason for this failure is that these explanations turn a potential risk factor into the cause of the problem.”

— Edwards MJ (2018)