Functional Neurologic Disorder (FND) is the second most common diagnosis in neurology clinics, following headaches. It involves symptoms caused by abnormal nerve function, yet no underlying disease or damage to the nerves or brain has been identified as the cause. These symptoms are entirely real and can vary widely.

Common symptoms include muscle weakness or paralysis, blackouts or non-epileptic seizures, and movement disorders such as tremors, muscle spasms, or jerky movements.

Other symptoms may include vision disturbances like double vision or vision loss, speech difficulties such as hoarseness, slurring, or stuttering, and altered skin sensation, including hemisensory syndrome (changes in sensation on one side of the body).

Dizziness and balance problems are also frequently reported.

The most likely explanation for FND is changes in key circuits within the brain, which disrupt normal function and lead to these symptoms.

If medical evaluations do not identify any disease or injury, or if treatments fail to provide expected improvement, it is likely that the brain plays a role in generating or contributing to the pain or illness. This is called a neuroplastic symptom.