Another indication of unilateral psychogenic leg weakness is Hoover sign (Fig. 3-2). Normally, when someone attempts to raise a genuinely paretic leg, the other leg presses down. The examiner can feel the downward force at the patient’s normal heel and can use the straightened leg, as a lever, to raise the entire leg and lower body. In contrast, Hoover sign consists of the patient unconsciously pressing down with a “paretic” leg when attempting to raise the unaffected leg and failing to press down with the unaffected leg when attempting to raise the “paretic” leg.

FIGURE 3-2 A neurologist demonstrates Hoover sign in a 23-year-old man who has a psychogenic left hemiparesis. A, She asks him to raise his left leg as she holds her hand under his right heel. B, Revealing his lack of effort, the patient exerts so little downward force with his right leg that she easily raises it. C, When she asks him to raise his right leg while cupping his left heel, the patient reveals his intact strength as he unconsciously forces his left “paretic” leg downward. D, As if to carry the example to the extreme, the patient forces his left leg downward with enough force to allow her to use his left leg as a lever to raise his lower torso.

FIGURE 3-3 Upper series: Left hemiparesis from a stroke with the examiner’s hands pushing the legs together, i.e., adducting them. A, When asked to abduct the left leg, that leg’s weakness cannot resist a physician’s pressure, which moves the leg toward the midline (adducts it). At the same time, the normal right leg reflexively abducts. B, When asked to abduct the normal right leg, it abducts forcefully. The paretic left leg cannot resist the examiner’s pressure, and the examiner pushes the leg inward. Lower series: Psychogenic left hemiparesis. C, When asked to abduct both legs, the left leg fails to resist the examiner’s hand pushing it inward (adducting it). In addition, because of the patient’s failure to abduct the right leg, the examiner’s hand also presses it inward. D, When asked to abduct the normal right leg, the patient complies and abducts it forcefully; however, the left leg, which has psychogenic weakness, reflexively resists the physician’s inward pressure and abducts – the abductor sign.

Gait Impairment

Many psychogenic gait impairments closely mimic neurologic disturbances, such as tremors in the legs, ataxia, or weakness of one or both legs. The most readily identifiable psychogenic gait impairment is astasia-abasia (lack of station, lack of base). In this disturbance, patients stagger, balance momentarily, and appear to be in great danger of falling; however, catching themselves at “the last moment” by grabbing hold of railings, furniture, and even the examiner, they never actually injure themselves (Fig. 3-4).

FIGURE 3-4 A young man demonstrates astasia-abasia by seeming to fall when walking, but catching himself by balancing carefully. He even staggers the width of the room to grasp the rail. He sometimes clutches physicians and pulls them toward himself and then drags them toward the ground. While dramatizing his purported impairment, he actually displays good strength, balance, and coordination.

Another blatant psychogenic gait impairment occurs when patients drag a “weak” leg as though it were a completely lifeless object. In contrast, patients with a true hemiparetic gait swing their paretic leg outward with a circular motion, i.e., “circumduct” their leg (see Fig. 2-4).

Sensory Deficits

Although the sensory examination is the least reliable portion of the neurologic examination, several sensory abnormalities indicate a psychogenic deficit. For example, loss of sensation to pinprick * that stops abruptly at the middle of the face and body constitutes the classic splitting the midline. This finding suggests a psychogenic loss because the sensory nerve fibers of the skin normally spread across the midline (Fig. 3-5). Likewise, because vibrations naturally spread across bony structures, loss of vibration sensation over half of the forehead, jaw, sternum, or spine strongly suggests a psychogenic disturbance.

FIGURE 3-5 A young woman with psychogenic right hemisensory loss appears not to feel a pinprick until the pin, which is used only for illustrative purposes, reaches the midline of her forehead, face, neck, or sternum (i.e., she splits the midline). When the pin is moved across the midline, she appears to feel a sharp stick.

A psychogenic sensory loss, as already mentioned, can be a discrepancy between pain and temperature sensations, which are normally carried together by the peripheral nerves and then the lateral spinothalamic tracts. Discrepancy between pain and position sensations in the fingers, in contrast, is indicative of syringomyelia (see Fig. 2-18). In this condition the central fibers of the spinal cord, which carry pain sensation, are ripped apart by the expanding central canal.

Testing for sensory loss when the arms are twisted, placed out of sight behind the patient’s back, or seen in a mirror may also expose psychogenic sensory deficits.

Finally, because sensory loss impairs function, patients with genuine sensory loss in their feet or hands cannot perform many tasks if their eyes are closed. Also, those with true sensory loss in both feet – from severe peripheral neuropathy or injury of the spinal cord posterior columns, usually from vitamin B₁₂ deficiency, tabes dorsalis, or MS – tend to fall when standing erect with their eyes shut. In other words, they have Romberg sign (see Chapter 2). By contrast, patients with psychogenic sensory loss can still generally button their shirts, walk short distances, and stand with their feet together with their eyes closed.

Special Senses

When cases of blindness, tunnel vision, diplopia, or other disorders of vision violate the laws of neuroanatomy, which are firmly based on the laws of optics, neurologists diagnose them as psychogenic. Neurologists and ophthalmologists can readily separate psychogenic and neurologic visual disorders (see Chapter 12).

A patient with psychogenic deafness usually responds to unexpected noises or words. Unilateral hearing loss in the ear ipsilateral to a hemiparesis is highly suggestive of a psychogenic etiology because extensive auditory tract synapses in the pons ensure that some tracts reach the upper brainstem and cerebrum despite central nervous system lesions (see Fig. 4-16). If doubts about hearing loss remain, neurologists often request audiometry, brainstem auditory-evoked responses, and other technical procedures.

Patients can genuinely lose the sense of smell (anosmia) from head injury (see Chapter 22), neurodegenerative disorders, or advanced age; however, these patients can usually still perceive noxious volatile chemicals, such as ammonia or alcohol, which irritate the nasal mucosa endings of the trigeminal nerve rather than the olfactory nerve. This distinction is usually unknown to individuals with psychogenic anosmia, who typically claim inability to smell any substance.

Other Conditions

A distinct but common psychogenic disturbance, the hyperventilation syndrome, occurs in people with an underlying anxiety disorder, including panic disorder. It leads to lightheadedness and paresthesias around the mouth, fingers, and toes, and, in severe cases, to carpopedal spasm (Fig. 3-6). Although the disorder seems distinctive, physicians should be cautious before diagnosing it because partial complex seizures and transient ischemic attacks (TIAs) produce similar symptoms.

FIGURE 3-6 Carpopedal spasm, which is the characteristic neurologic manifestation of hyperventilation, consists of flexion of the wrist and proximal thumb and finger joints. Also, although the thumb and fingers remain extended, they are drawn together and tend to overlap.

In this syndrome, hyperventilation first causes a fall in carbon dioxide tension that leads to respiratory alkalosis. The rise in blood pH from the alkalosis produces hypocalcemia, which induces the tetany of muscles and paresthesias. To demonstrate the cause of the spasms, physicians may recreate them by having a patient hyperventilate. This procedure may also induce giddiness, anxiety, or confusion. The conventional wisdom dictates that, if hyperventilation causes those symptoms, the physician should abort the demonstration by having the patient continually rebreathe expired air from a paper bag cupped around the mouth. However, that remedy does not stop such attacks and, moreover, physicians employing it might mistakenly put a bag to the face of people breathing rapidly because of an asthma attack or congestive heart failure.

Potential Pitfalls

The examination of a patient suspected of having a psychogenic deficit requires particular sensitivity. It need not follow the conventional format and can be completed in two or more sessions. A threatening, embarrassing, or otherwise inept evaluation may obscure the diagnosis, harden the patient’s resolve, or precipitate a catastrophic reaction.

An unreliable indication of a psychogenic deficit is a patient’s absence of concern or affect, la belle indifférence, concerning it. This emotional posture is now known as a potential manifestation of any neurologic disorder, but particularly hemi-inattention, Anton syndrome, and frontal lobe injury. Physicians should give la belle indifférence no credibility.

Although the neurologic examination itself seems rational and reliable, some findings are potentially misleading. For example, many anxious or “ticklish” individuals, with or without psychogenic hemiparesis, have brisk deep tendon reflexes and extensor plantar reflexes. Another potentially misleading finding is a right hemiparesis unaccompanied by aphasia. In actuality, a stroke might cause this situation if the patient were left-handed, or if the stroke were small and located in the internal capsule or upper brainstem (i.e., a subcortical region). With a suspected psychogenic left hemiparesis, physicians must assure themselves that the problem does not actually represent left-sided inattention or neglect (see Chapter 8).

Neurologists tend to misdiagnose several types of disorders as psychogenic when they are unique or bizarre, or when their severity is greater than expected. This error may simply reflect an individual neurologist’s lack of experience.

They also may misdiagnose disorders as psychogenic when a patient has no accompanying objective physical abnormalities. This determination might be faulty in illnesses where objective signs are often transient or subtle, such as MS, partial complex seizures, and small strokes. If given an incomplete history, neurologists may not appreciate certain disorders, such as transient hemiparesis induced by migraines, postictal paresis, or TIAs, or transient mental status aberrations induced by alcohol, medications, or seizures (see Box 9-3).

Another potential pitfall is dismissing an entire case because a patient is grossly exaggerating a deficit. Patients may feel that they must overstate a genuine medical problem to gain the necessary attention. In addition, the prospect of having developed a neurologic disorder may trigger overwhelming anxiety. For example, patients with a persistent headache may so fear a brain tumor that they embellish their history with additional symptoms to obtain a MRI.

Possibly the single most common error is failure to recognize MS because its early signs tend to be evanescent, exclusively sensory, or so disparate as to appear to violate several laws of neuroanatomy. Neurologists can usually make the correct diagnosis early and reliably – even in ambiguous cases – with MRIs, visual-evoked response testing, and cerebrospinal fluid analysis (see Chapter 15). On the other hand, trivial sensory or motor symptoms accompanied by normal variations in these highly sensitive tests may lead to false-positive diagnoses of MS.

Neurologists are also prone to err in diagnosing involuntary movement disorders as psychogenic. These disorders, in fact, often have some stigmata of psychogenic illness (see Chapter 2). For example, they can appear bizarre, precipitated or exacerbated by anxiety, or apparently relieved by tricks, such as when walking backwards alleviates a dystonic gait. Also, barbiturate infusions usually temporarily reduce or even abolish involuntary movements. Because laboratory tests are not available for many disorders – chorea, tics, tremors, and focal dystonia – the diagnosis rests on the neurologist’s clinical evaluation. As a general rule, physicians should assume, at least initially, that movement disorders are not psychogenic (see Chapter 18).

Physicians often misdiagnose epilepsy and PNES in both directions (see Chapter 10). In general, episodes of PNES are clonic and unaccompanied by incontinence, tongue biting, or loss of body tone (Fig. 3-7). Furthermore, while exceptions occur, patients tend to regain awareness and have no retrograde amnesia immediately after the movements cease. On the other hand, both frontal lobe seizures and mixtures of epileptic and psychogenic seizures notoriously mimic purely psychogenic ones. EEG-video monitoring during and between episodes is the standard diagnostic test.