Case of the Month #14: Functional Neurological Disorder by Dr Sonia Pierce

Functional neurological disorder (FND) is a common cause of persistent, disabling neurological symptoms. The symptoms are varied and may include abnormal control of movement, episodes of altered awareness resembling epileptic seizures and abnormal sensation1. Chronic pain, fatigue and cognitive symptoms commonly feature in addition. The symptoms are genuinely experienced and related to a functional, rather than a structural disorder2. No single mechanism has been identified to explain the onset of FND, but several complex interacting biological, psychological and social factors are likely to contribute. Injury and pain can be a common trigger for FND flare-ups. Anxiety, depression and traumatic life experiences can also contribute to making brains more vulnerable to FND.

Functional seizures and dissociative events are common. These episodes involve altered movements, sensations or experiences that closely resemble epileptic seizures, but are not associated with electrical discharges in the brain. The most common symptoms are excessive movements of limbs, trunk and head. Stiffening, tremor, muscle weakness and loss of responsiveness may also occur. The episodes often can be precipitated by mental, physical (including sensory overload) or social stressors. Dissociation can involve feeling disconnected from the body (e.g., thoughts, feelings, sensations) and/or disconnected from the surroundings. People often describe dissociation as feeling spacey, zoning out, or as though the brain has shut down. Patients suffering from a functional neurological disorder often have chronic pain and other symptoms such as fatigue and difficulty with cognitive function and sensory symptoms such as numbness and tingling are common1,2.

An assessment for someone with probable FND should include a thorough review of presenting symptoms and history of onset as well as other symptoms including fatigue, sleep disturbance, pain and concentration symptoms. Psychological assessment and formulation may reveal a much more complex picture than initially apparent. Evaluation can help patients and therapists understand predisposing, precipitating and perpetuating factors. Patients with FND have often been through negative experiences of healthcare, including being disbelieved2. It is useful to spend time hearing about those experiences and finding out what the patient, and those around them, think would be most helpful now. As in this case, a diagnosis of FND is usually made by a neurologist. Normal scans and tests help but the diagnosis is usually made at the bedside on the basis of positive clinical signs. Limb weakness in FND is most commonly unilateral and patients typically report a feeling that the limb doesn’t belong to them. There may be a difference between the examination of power, for example, on the bed and when walking. Some people with functional weakness have relatively normal examination of strength in the legs on the bed but weak legs when walking but the reverse can also be true. This is not because they are not trying, the variability is a key feature of the diagnosis. Hoover's sign and hip abductor sign are the most reliable 2. Hoover's sign is positive if there is weakness of hip extension, which returns to normal with contralateral hip flexion against resistance. The hip abductor sign is similar test showing discrepancy between voluntary and automatic hip abduction strength.

This patient’s chronic pain and functional neurological symptoms are complex, and the team felt she benefitted from a detailed assessment by the multidisciplinary pain team. FND is a chronic condition with multiple contributing factors, and thus ongoing support and follow-up will often be necessary1. Our pain management team is currently working with a group of other professionals to develop a service for patients with FND, which we hope will better meet the needs of patients like this in the future.