Functional Neurological Disorder (FND) involves symptoms like weakness, tremor, or seizures that appear neurological but are not caused by underlying structural damage or a traditional disease process of the nervous system. The symptoms are genuine and involuntary, stemming from a problem in the functioning of the nervous system rather than its physical structure. Diagnosing this condition requires specialized neurological expertise, moving beyond simple exclusion to actively identify specific patterns indicative of a functional disorder. This diagnostic journey is essential for validating the patient’s experience and directing them toward appropriate, targeted treatment.
The Role of Clinical History and Neurological Examination
The diagnostic process begins with a comprehensive clinical history taken by a neurologist, focusing on the symptoms themselves. Specialists pay close attention to the onset of symptoms, looking for a sudden beginning or a presentation that may have been triggered by a physical injury, high stress, or emotional distress. A detailed history also helps to establish the variability of the symptoms, noting if they fluctuate in severity throughout the day or disappear completely during certain activities.
The physical examination is designed to look for inconsistencies that do not align with known neurological diseases. For instance, a patient with functional weakness might drag their entire limb in a non-specific manner, which is incongruent with the typical walking patterns seen in conditions like stroke. This initial assessment is crucial for establishing the functional nature of the symptoms, as organic diseases generally present with signs that are consistent and predictable based on neuroanatomy.
Excluding Other Neurological Conditions
A thorough workup for Functional Neurological Disorder involves ruling out diseases that mimic FND symptoms, such as multiple sclerosis, epilepsy, or stroke. This step confirms that the symptoms are not caused by a structural lesion or organic disease process. The neurologist may order standard diagnostic tests, including neuroimaging like a brain MRI or CT scan, to check for structural abnormalities in the central nervous system.
Blood panels may also be used to exclude metabolic, infectious, or autoimmune causes that could explain the neurological symptoms. For seizure-like episodes, a video-EEG (electroencephalogram) is often performed to confirm the absence of epileptic electrical activity in the brain during an event. The results of these tests are expected to be normal or inconsistent with the patient’s reported disability, confirming that the problem lies in the nervous system’s functioning, not its physical integrity.
Identifying Specific Positive Diagnostic Signs
Unlike many diagnoses that rely on the absence of other findings, FND is confirmed by the presence of specific, observable positive signs characteristic of a functional disorder. These signs demonstrate an internal inconsistency or incongruity in the patient’s motor or sensory system. The most well-known example is Hoover’s Sign, which tests for functional leg weakness.
In Hoover’s Sign, the patient is asked to press their “weak” heel down against the examiner’s hand, which they cannot do voluntarily. However, when the patient is distracted by being asked to lift their other leg against resistance, the examiner feels an involuntary, normal downward pressure from the “weak” leg. This suggests the motor pathway is physically intact, but the voluntary access to it is compromised.
Another important sign is the entrainment phenomenon, used to diagnose functional tremor. The entrainment test involves asking the patient to tap a rhythm with their unaffected limb while their affected limb is trembling. In a functional tremor, the tremor’s frequency or rhythm will often change, stop, or become synchronized (entrained) to the tapping rhythm of the opposite limb.
This distractibility and variability indicates a functional issue. Tremors caused by degenerative diseases like Parkinson’s disease generally remain consistent regardless of distraction. Other signs include collapsing weakness, where the muscle strength suddenly gives way when tested, and a highly variable resistance to passive movement. The identification of these positive signs provides the definitive evidence for a confident FND diagnosis.
Formalizing the Functional Neurological Disorder Diagnosis
The diagnosis of Functional Neurological Disorder is formally made by a neurologist who synthesizes the consistent clinical history, the negative results from exclusionary tests, and the presence of these specific positive physical signs. This combination of evidence allows the clinician to confidently establish the diagnosis. The final step involves communicating the diagnosis clearly and empathetically to the patient.
It is important for the neurologist to convey that FND is a genuine, common neurological condition and that the patient’s symptoms are real and not imagined. Providing a clear explanation of how the diagnosis was reached, specifically referencing the positive signs, helps the patient understand the nature of their disorder. This transparent communication is foundational for patient acceptance and prepares the patient for subsequent treatment.