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  • Updated 04.09.2024
  • Released 04.18.2001
  • Expires For CME 04.09.2027

Functional neurologic disorders and related disorders



This topic reviews functional neurologic disorder, Munchausen syndrome, Munchausen syndrome by proxy, and Ganser syndrome. These behavioral disorders are related by their (1) resemblance to other, more familiar neurologic disorders; (2) lack of established biomarkers (eg, specific structural lesions on brain imaging studies, seizure waveforms on EEGs); and (3) aggravation of symptoms or those reported by a caregiver from the patient’s or caregiver’s attention to the disorder. However, the features and causes for these disorders are very different from each other and are reviewed. This topic also reviews several widespread manifestations of functional neurologic disorder, including Havana syndrome (now called “anomalous health incident”), mass psychogenic illness that is disseminated by social media, and postvaccination functional neurologic disorder, in particular following COVID disease vaccination. For functional neurologic disorder, new biomarkers are being intensively investigated.

Key points

• Functional neurologic disorders are commonly encountered in general neurologic practices and, hence, knowing their manifestations and treatment is crucial for clinical care.

• The disturbance is involuntary, and yet at the same time it can be intermittently improved by the patient, depending on the patient’s reducing attention to the deficits.

• Although it can be improved intermittently by the patient, the disturbance is generally disabling unless expert professional care intervenes.

• There is no consistent association between functional neurologic disorders and either posttraumatic emotional stress, psychiatric disease, or sexual abuse.

• The mistaken diagnosis of Munchausen syndrome by proxy (the intentional false reporting of illness by caregivers of dependent individuals) has led to legal or criminal actions in recent years, either by the dependent individual or family members.

• Havana syndrome, a purported acute brain injury resulting from exposure to either microwave or subsonic waves from weapons directed at diplomacy employees, has been found not to have a specific neuropathology. This raises the question of whether traumatic brain injury is responsible. Functional neurologic disorder is the more plausible explanation.

Historical note and terminology

"Hysteria" was the original term for fluctuating and disabling neurologic disorders in alert sufferers, which were attributed from classical times to a "wandering uterus" because of their predominance in women (314). Offray de La Mettrie, for example, published in 1738 an account of episodic catalepsy (waxy immobility of the limbs) in a woman that he attributed to hysteria arising from amenorrhea (301). Eighteenth century treatments for hysteria were radical and untested, including bloodletting, beatings, diet, fresh air, and writing (185).

Broca’s 1861 seminal and replicated discovery that aphasia follows from focal lesion in the brain as found on autopsy, more often in the left cerebral hemisphere, inspired subsequent neuroscientists to trace other neurobehavioral disorders to their respective specific brain regions (see the MedLink article, “Nonprogressive aphasia”). Broca’s contemporary neuroscientist Briquet related functional neurologic disorders of both women and men also to cerebral disease, but in contrast to aphasia, these disorders did not leave visible lesions at autopsy (68). Nonetheless, Briquet relocalized functional neurologic disorders from the uterus to the brain. Reynolds published in 1869 a prescient overview of functional movement or sensory disorders that appeared to be based on an ideological fixation and were amenable to compassionate behavioral retraining (224). In 1888 Blocq comprehensively described a case series of the acute inability to stand and walk despite full motor control of the legs while the patients were supine, which he termed “astasia-abasia,” a term that continues today (201). Although he doubted that the disturbance had a purely psychologic etiology, his pathophysiologic hypothesis—that marked emotional distress can aggravate cerebral inhibition over spinal walking mechanisms—is remarkably similar to current pathophysiologic hypotheses for functional disturbances. Late in his career, Charcot opined that functional disorders emanated from focal disturbances of the nervous system, but which did not affect a specific part of the body. Therefore, Charcot hypothesized that functional neurologic disorder did not seem to result from a consistent structural central nervous system lesion. Instead, he postulated that functional neurologic disorder may emerge from an anatomically “dynamic” lesion, for which extant neurologic examination techniques could not identify (110).

Near the end of the 19th century, Freud (who trained as a neurologist under Charcot and observed his demonstrations of hysteria in his patients) hypothesized that an unconscious and involuntary cognitive process called “conversion” caused functional neurologic disorders (48; 98). In this model, emotionally conflicting memories of young life abuse or other upsetting personal experiences are involuntarily repressed and “converted” to severe somatic involuntary disturbances. Although no experimental evidence for this process was adduced for this nonfalsifiable model, this concept became firmly established and continues today in contemporary medical care (58). Commonly, functional neurologic disorder is called “conversion disorder,” including in present-day medical diagnostic classifications for clinical billing.

A surge of interest in functional neurologic disorders came with World War I, when European soldiers returned from combat with a variety of fluctuating neurologic deficits without traumatic brain injury (134; 165). These post-combat disorders were considered to be neurologic, even though their precise etiologies were unclear. However, the neurologic interest in the causes, physiologic basis, and treatment of functional disorders became overshadowed, for the most part, by the successful outcomes of the psychoanalysis that was developed by Freud (68). Over the 20th century, the lack of rigorous empirical evidence for unconscious repression led to a return of interest to the neurophysiological basis of functional disorders, beginning in the 1960s, and continues to the present.

A wide variety of synonyms for these disorders have been used up to the present, which hampers understanding. These terms include hysteria, conversion disorder, medically unexplained disorder, shell shock, combat neurosis, psychogenic neurologic disorder, and pseudoseizure. Edwards and Bhatia emphatically recommended the term “functional neurologic disorder” on the grounds that patients find this less objectionable than rival terms (274; 80), which helps to emphasize the reversibility of the disorder (223; 268). PubMed shows a continually increasing adoption of this term since 2005. The term “anomalous health incidents” has been introduced in the medical literature, referring to “the abrupt onset of disruptive symptoms including dizziness, pain, visual problems, and cognitive dysfunction” according to the United States Government, and replaces the term “Havana syndrome” (Chan et al in press; Pierpaoli et al in press).

"Somatization disorder" or "Briquet syndrome" is a variant of functional disorder in which diverse bodily complaints (eg, fatigue, insomnia, irritable bowel) occur without resembling specific neurologic disorders and without objective physiologic evidence (143; 268). "Malingering" is the fully aware simulation of a medical disorder (frequently neurologic) for personal gain, particularly for money, material goods, or improved access to specific privileges (eg, transfer from jail). "Factitious disorder" is the willful simulation of a medical disorder without clear financial or opportunistic gain (23). Instead, sufferers have a need for an enhanced feeling of control or attention. "Munchausen syndrome" is a variant of factitious disorder (often with diverse complaints), in which the patient undergoes frequent clinic or hospital evaluation, sometimes resulting in invasive, even injurious, testing or treatment. The term was coined by Asher (12), who thought that the wide meanderings of afflicted patients from clinic to clinic and their elaborate health histories resembled the fantastic travels regaled by a fictitious character depicted by Raspe in 1785, Baron Munchausen (206). (This individual was likely inspired by the real Baron Münchhausen; consequently, German spellings of this disorder also appear.) "Munchausen syndrome by proxy" refers to a caregiver's bearing false evidence of medical illness in another individual who is incompetent to represent himself (a child, in most cases described thus far) (184). Ganser syndrome involves the inconsistent confabulation of knowledge of facts (101).

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