Functional (Psychogenic) Neurologic Disorders

Introduction

A functional neurologic disorder (FND) is any type of neurologic disorder that arises from dysfunction of the brain when normal function is possible. The name of this disorder has changed over the years. Previously called hysteria and conversion disorder , it then became psychogenic neurologic disorder , and only in recent years has the terminology changed to functional neurologic disorder . The change is due to several factors. First, while psychologic factors often seem etiologically relevant, such factors cannot always be identified, and the pathophysiology is not fully understood. Second, patients are more accepting of the diagnostic label, and acceptance of the diagnosis is the first step in treatment.

FNDs fall between neurology and psychiatry. Patients present to neurologists with neurologic symptoms, but the usual treatments have been psychiatric. Neither specialty took an interest in these patients, who were largely neglected in the latter part of the twentieth century when neither neurologists nor psychiatrists were being trained to diagnose and treat them. Fortunately, the situation is changing. In the psychiatric classification DSM-5, “functional neurologic symptom disorder” or “conversion disorder” falls under somatic symptom and related disorders. To make the diagnosis, manifestations need to be inconsistent and incongruent with other neurologic disorders and cause the patient distress. Such formal recognition is important.

FNDs are common. Neurologic practices vary, but typically FND is the second most common diagnosis after headache, accounting for 10 to 30 percent of patients. Women are affected more often than men. The diagnosis in the past was largely based on excluding other neurologic disorders, but the emphasis now is on the identification of positive features. FNDs may accompany other neurologic disorders, thus complicating their diagnosis. For example, many patients with multiple sclerosis also have functional symptoms, and patients with an established seizure disorder can also have functional seizures.

Clinical Features of Functional Neurologic Disorders

As with any other neurologic disorder, the key to diagnosis of FND involves careful assessment of findings detected on neurologic examination, combined with clues from the clinical history. Of critical importance is that the diagnosis of FND is made on the basis of positive findings, not merely one in which other “organic” diseases are excluded ( Table 52-1 ). Positive findings suggestive of a diagnosis of FND are discussed below.

Table 52-1

Positive Signs on Neurologic Examination in Functional Neurologic Disorders

General Features

Inconsistency

Distractibility

Suggestibility

Functional Weakness

Drift without pronation

Hoover sign

Collapsing/give-way weakness

Functional Parkinsonism

Excessive slowness without decrement in speed or amplitude on repetitive tapping

Variability in tone during passive manipulation

Functional Tremor

Variable frequency

Entrainment or suppressibility of tremor with externally cued movement

Pause with contralateral ballistic movement

Functional Dystonia

Resistance to passive manipulation

Lack of sensory trick

Face region: tonic lateral deviation of lips or jaw to one side

Face region: concurrent contraction of orbicularis oculi and contralateral frontalis

Functional Gait/Posture

Better balance than claimed

Excessive gait slowness

Dragging monoplegic gait

Knee buckling

Absence of falls despite excessive sway during gait

Excessive demonstration of effort

Inconsistent, noneconomic posture

Functional Speech and Voice

Effortful speech

Excessive variability in severity during different speech examination activities

Functional Sensory Symptoms

Splitting of vibration across forehead or sternum

Precise midline splitting of sensory deficit

Tubular visual field defect

Motor Disorders

Features suggestive of functional motor disorders include an abrupt onset of symptoms and inconsistency of the abnormal movements. Symptoms may rapidly vary in terms of severity, disappearing with distraction and increasing with attention. Diagnosis is based upon demonstration of motor inconsistency (i.e., varying symptoms with susceptibility to distraction) and/or incongruence (i.e., movements that are incompatible with normal physiologic patterns).

Several features on neurologic examination can point to a diagnosis of functional weakness. Drift without pronation of the weak arm, Hoover sign, dragging monoplegic gait, and collapsing or give-way weakness are all positive signs suggestive of functional weakness. Hoover sign relies on contralateral synkinetic oppositional mirror movements, and is deemed to be positive when weakness of hip extension is corrected upon flexion of the contralateral hip against resistance. Dragging monoplegic gait describes a gait in which the leg is dragged with the knee extended and the ipsilateral hip either externally or internally rotated; this contrasts with the circumduction observed in the setting of organic leg weakness. Collapsing or give-way weakness describes the demonstration of strength followed by sudden collapse. It is important to note that the validity of these signs is variable. Collapsing weakness, for example, can also be seen in patients with pain or with difficulty following instructions in addition to those with functional weakness.

Functional excess movements can include functional tremor, dystonia, and myoclonus, among others. Functional tremor is characterized by its variable frequency and distractibility. The “entrainment test” is commonly used in the diagnosis of functional tremor and highlights its variable frequency. In this maneuver, the patient performs an externally cued rhythmic movement, with resulting suppression or altered frequency of the functional tremor. Features suggestive of functional dystonia include abrupt onset, fixed posture present from early in the course of the disease, and resistance to manipulation. Pain commonly accompanies functional dystonia, and sensory tricks are rare. Functional dystonia involving the cranial region can present with lateral deviation of the mouth, including the lower lip, jaw, and tongue. When functional dystonia involves the eye, spasm of the orbicularis oculi with contraction of the contralateral frontalis muscle may be seen.

Functional parkinsonism can present with excessive slowness in the absence of decrement of repetitive movements, as well as normal speed when spontaneous movements are performed. Inconsistent rigidity and functional tremor may also be present.

Axial Disorders

Functional disorders of gait and posture are commonly seen in patients with FNDs. Features suggestive of functional gait include excessive gait slowness, noneconomic posture, astasia-abasia, sudden knee buckling, and excessive demonstration of effort, referred to as the “huffing and puffing sign.” Functional postural abnormalities include propriospinal myoclonus, involving myoclonic-like jerks affecting the trunk.

Nonepileptic Seizures

Nonepileptic seizures (NESs) are the most common type of FND. Differentiating between NES and epileptic seizures (ESs) can be challenging. One difficulty is that the disorder is paroxysmal, and examination of the patient may well be normal. It is important to see an event, and a family member or friend should be asked to video the event if this has not been done already. Signs that may help to reliably distinguish NES from ES include long duration, fluctuating course, eye closure at onset, eye fluttering, ictal crying, memory recall, and preserved awareness. The presence of pelvic thrusting and asynchronous or side-to-side movements may also be used to reliably distinguish NES from ES, with the caveat that frontal-lobe partial seizures can also present with these signs. Although history-taking in patients with seizures often includes questions about the presence of urinary incontinence and tongue biting, these features do not reliably distinguish between ES and NES.

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