General Overview of Psychogenic Movement Disorders: Epidemiology, Diagnosis, and Prognosis

Anthony E. Lang

ABSTRACT

Epidemiologic studies of “medically unexplained symptoms” are fraught with problems. Despite numerous confounding issues, it is clear that conversion disorders are probably as common as other disabling conditions such as multiple sclerosis and schizophrenia. Little is known about the frequency of movement disorders as a manifestation of conversion disorders. Reports from subspecialty clinics all suffer from ascertainment as well as selection/referral biases with an underrepresentation of acute or transient cases and overrepresentation of chronic or refractory problems. Although underlying neurologic diseases need to be carefully excluded when dealing with such patients, the diagnosis itself is not one of exclusion. Certain historical features are common to many different types of psychogenic movement disorders (PMDs), including abrupt onset (often triggered by a minor injury for which litigation or compensation is sought), rapid progression to maximum disability or peak severity shortly after onset, static course, previous remissions, and paroxysmal exacerbations. Clinical features common to most PMDs are the incongruity with their organic counterparts and inconsistencies during the examination, over time or with historical information provided. Additional “nonorganic” neurologic disturbances are also common, including give-way weakness, nonanatomic sensory disturbances, atypical pain syndromes, and extreme slowness of movement. Investigations may not be helpful (except for excluding specific underlying organic disorders), although electrophysiologic testing may be particularly useful in confirming the diagnosis in some PMDs, especially myoclonus and tremor. The diagnosis should not be made or refuted by physicians inexperienced in the investigation and management of both organic and psychogenic movement disorders. In the presence of clear positive confirmatory clinical features, the diagnosis should not be excluded on the basis of the screening psychiatric assessment failing to define the presence of underlying psychopathology. The natural history of PMDs is poorly defined, but often patients remain disabled over prolonged periods of time. Review of the appropriate literature highlights the need for considerable future research to establish a better understanding of all facets of PMDs including epidemiologic features, diagnostic methodologies, pathogenetic mechanisms, and, particularly, more effective treatment strategies.

In this chapter, I will provide an introductory discussion of several issues common to all psychogenic movement disorders. Specifics related to individual types of movement disorders will be covered in more detail in subsequent chapters. At the outset, it must be admitted that there is no consensus on diagnostic terminology. A variety of terms including hysterical conversion, somatoform disorders, “functional” symptoms, medically unexplained symptoms, and so on, have been applied. Although the term “psychogenic” is common in the movement disorder literature, it obviously has negative connotations for patients. The term “medically unexplained” is similarly considered pejorative, and Stone et al. have argued for a return to the use of “functional” to describe these problems (1). Another point that should be mentioned briefly is the fact that the term “movement disorders” is not necessarily widely recognized outside the field of neurology, and therefore it is quite uncommon for such patients to be distinguished or separated from the larger group of patients with “unexplained motor symptoms,” where absence of motor function (e.g., hemiplegia, paraplegia) predominates. In fact, some follow-up studies have purposely excluded patients with abnormal motor activity “because of the risk of including patients whose symptoms might have an organic cause” (2). Another major problem in studies involving psychogenic movement disorders is the general lack of a gold standard by which a diagnosis can be established. In fact, a large proportion of movement disorders (particularly those designated as “idiopathic”) lack any defining laboratory, electrophysiological, or imaging abnormalities. A relatively high proportion of patients seen by movement disorder experts do not fulfill the criteria for a “documented” psychogenic movement disorder, but instead are categorized as “clinically established” largely based on a variety of features that are felt by the clinician to be incongruent with established organic disorders or variably inconsistent by history and examination (3). Recognizing this, Williams et al. suggested that these two categories be combined to form the category of “clinically definite” (4). In the absence of defining diagnostic measures (aside from clinical features), a number of studies have characterized the frequency of the historical and clinical features in various psychogenic movement disorders which were diagnosed in large part on the basis of the presence of these features (i.e., a problem of self-fulfilling prophecy). This especially creates problems when some investigators feel that specific clinical features support a psychogenic origin, while others feel that the same features are characteristic of an established organic syndrome. The best example of this is the case of posttraumatic dystonia with or without associated complex regional pain syndrome (see Chapter 8).

PREVALENCE

There are numerous studies evaluating the epidemiology of somatoform disorders. As pointed out by Akagi and House (5), these are generally fraught with a variety of problems which these authors have subdivided into questions of case definition, case ascertainment, and selection of a suitable population to study. As mentioned above, specifically with respect to psychogenic movement disorders, the lack of confirmatory diagnostic testing compromises case definition even when the clinical criteria are adequate and rigidly applied. Case ascertainment is particularly confounded by the wide range of medical practices assayed (e.g., general practice, emergency room, neurology, or psychiatry in- or outpatient services, etc.) and the inclusion of acute versus chronic cases. Finally, applying the usual epidemiologic approach of defining a target population from which the study population is chosen and then taking an appropriate sample is generally not possible from the available literature, although one recent small study from Florence did attempt to utilize this format (6). Despite these confounding issues, it is clear that somatoform disorders or medically unexplained symptoms are probably as common as other disabling conditions such as multiple sclerosis and schizophrenia (5). It has been suggested that up to 50% of patients seen in specialty clinics or seeking secondary medical care can be classified as such (7, 8, 9) and as many as 30% to 40% of patients attending general neurology clinics have symptoms that are either not at all explained or only somewhat explained by organic disease (8,10, 11, 12). In patients who most frequently attend outpatient services, one study found that 27% had one or more consultation episodes in which the condition was medically unexplained, and 21% of all consultations were medically unexplained (13).

Epidemiologic studies of psychogenic movement disorders are lacking. All available reports originate from tertiary academic movement disorder clinics, and therefore it is impossible to say how common these disorders are in the community at large or even how common they are with respect to neurological conversion disorders in general. In the only series that divided medically unexplained motor symptoms into “absence of motor function” and “presence of abnormal motor activity,” 48% had index symptoms in the former category, while 52% had symptoms such as tremor, dystonia, and ataxia (14). However, these figures may have been influenced by referral bias since Professor C. David Marsden was one of the senior authors. Factor et al. found that 28 of 842 (3.3%) consecutive movement disorder patients seen over a 71-month period were diagnosed as having a documented or clinically established psychogenic movement disorder (15). [A recent update of
these numbers gave an almost identical figure: 135 of 3,826 (3.5%); S. Factor, personal communication, 2003.] Most other studies have described either the relative frequencies of specific subtypes of psychogenic movement disorders or have only indicated the proportion of patients with a specific subtype of movement disorder phenotype diagnosed as psychogenic (e.g., the proportion of all patients presenting with dystonia diagnosed as psychogenic). Obviously, even here, referral biases will have a great influence on the results. Tertiary care movement disorder clinics tend to see the more complex or difficult-to-diagnose cases. These clinics will also tend to accumulate more chronic or refractory cases, while patients with acute and short-lived symptoms (which typically have a better prognosis as outlined below) are less likely to be seen. In addition, the caseload of certain clinics may be influenced by their research interests. For example, the designation of Columbia Presbyterian Medical Center as a Dystonia Medical Research Foundation Center of Excellence may have partially accounted for the higher proportion of patients with psychogenic dystonia (54%) (4) compared to most other centers (25% to 28%) (Table 5.1). Considering all of these possible biases, Table 5.1 provides a summary of the relative frequencies of various psychogenic movement disorders as seen in several subspecialty clinics. A noncomprehensive review of the database from the Toronto Western Hospital Movement Disorders Clinic found a high likelihood of the psychogenic etiology (i.e., “clinically definite”) in 154/1,115 (13.8%) patients with tremor (excluding Parkinson disease), 91/1,078 (8.4%) with dystonia, 65/209 (31.1%) with myoclonus, 6/218 (2.8%) with chorea, 8/44 (18.2%) with nonspecified gait disturbance and 16/2,845 (0.6%) with parkinsonism.

TABLE 5.1 COMBINED DATA ON PSYCHOGENIC MOVEMENT DISORDERS SEEN AT SEVERAL MOVEMENT DISORDER CENTERS^a

Psychogenic Movement Disorder	Toronto (Toronto Western Hospital)^b	New York (Columbia Presbyterian Medical Center)^c	Cleveland Clinic Florida^d	Albany Clinic^e	Paris^f	Chicago (Rush Medical College)^g	8 Spanish University Centers^g	Baylor College of Medicine	Total
	(%)	(%)	(%)	(%)	(%)	(%)	(%)	(%)	(%)
Dystonia	91 (27)	82 (54)	14 (25)	30 (24)	20 (27)	25 (28)	14 (29)	89 (39)	365 (31)
Tremor	154 (45)	21 (14)	18 (32)	60 (47)	22 (29)	42 (48)^h	23 (48)^h	127 (56)	467 (40)
Myoclonus	65 (19)	11 (7)	4 (7)	17 (13)	0	11 (12)	8 (17)	30 (13)	146 (13)
Parkinsonism	16 (5)	3 (2)	0	11 (9)	9 (12)	12 (14)ⁱ	3 (6)ⁱ	6 (3)	60 (5)
Gait disorder	8 (2)	14 (9)	1 (2)	0	19 (25)	41 (47)^j	24 (50)^j	7 (3)	114 (10)
Tics	0	2 (1)	2 (4)	3 (2)	1 (1)	6 (7)	0	15 (7)	29 (2)
Other	6 (2)	19 (13)	17 (30)	6 (5)	4 (5)	10 (11)	1 (2)	1 (0.4)	64 (5)^k
Total	340	152	56	127	75	147	73	275	1,245
^aVarious approaches have been used in the collection of this data. Some centers (see g) have listed all movements evident (therefore, the combination of the numbers of patients demonstrating movement disorder subtypes will be larger than the total number of patients seen) and others (b-f) have listed only the dominant movement disorder syndrome demonstrated by the patient. These numbers are combined only to provide a very rough estimate of the frequency of the different movement disorder phenotypes seen in patients with psychogenic movement disorders. ^bToronto Western Hospital (listed only predominant movement) (AE Lang, personal observations, 2003). ^cColumbia Presbyterian Medical Center (listed all types of movement; 131 patients) (4); patients’ symptoms were classified as dystonia (rather than placed in another category) if any dystonic features were present. In most other series, patients were classified according to the predominant movement disorder. ^dCleveland Clinic Florida (listed only the predominant movement, 1998-2002) (N Galvez Jiminez, personal observations). ^eAlbany Clinic—updated from Factor SA, Podskalny GD, Molho ES. Psychogenic movement disorders: frequency, clinical profile, and characteristics. J Neurol Neurosurg Psychiatry. 1995;59(4):406-412, with permission; S. Factor, personal communication, see this volume; listed only the predominant movement—83 definite, 39 probable, 5 possible. ^fM. Vidailet, personal communication; listed only the predominant movement; seen over six years from a database of 4,400 patients with various movement disorders. ^gSee E. Cubo et al. in this volume; listed all movements present. ^hAction tremor only included here (rest tremor also listed in data presented, overlapped with action tremor). ⁱListed as “bradykinesia.” ^jAny gait disorder, not necessarily the primary problem. ^kOthers (n): chorea (11), blepharospasm/facial movements (8), “cerebellar” (4), “dyskinesias” (3), “stereotypies” (1), ballism (1), athetosis (1), stiff person (1), other (34).