Gender Differences in Functional Movement Disorders

ABSTRACT

Background

Functional neurological disorders are generally more common in females than males, but the reason for this gender difference is not well understood.

Objectives

In this study, we aim to compare the clinical and demographic features of functional movement disorders (FMDs) between males and females.

Methods

We examined clinical data and video‐recordings of patients with FMDs evaluated at the Baylor College of Medicine Movement Disorders Clinic.

Results

Of the 196 patients with FMDs, males represented only 30% (n = 59) of the entire cohort. Men had an older age at onset: 40.5 versus 34.1 years (P = 0.026) and an older age at evaluation: 43.8 versus 38.1 years (P = 0.041) compared to women. Functional dystonia was more frequently observed in women: 47.5 versus 20.3% (P < 0.001), but there was a trend for higher frequency of functional gait disorder in men: 44 versus 30% (P = 0.056). Females were particularly over‐represented (73.7%) in children and adolescents; but the genders were equally represented in patients aged ≥50 years.

Conclusions

Female patients are over‐represented in FMDs, except in individuals aged ≥50 years. Compared to female patients, males with FMDs present later in life and are less likely to have functional dystonia.

Functional neurological disorders (FNDs) have been recognized for millennia, mainly under the term “hysteria,” derived from the Greek word for uterus, a concept introduced in the corpus Hippocraticum that the uterus moves inside a woman's body (“wandering womb”) eventually suffocating her.1 The higher prevalence of FND in females led several medical authorities over the millennia to develop theories relating the FNDs with the uterus, reinforcing the usage of the term hysteria and giving exclusivity of this group of disorders to the female gender. It was not until the 17th century that the pathogenic theories of FNDs shifted from emphasis on the uterus to the brain and mind.1, 2 This permitted the recognition that the uterus was not necessary for the development of hysteria, and therefore it may also occur in males. Paul Briquet, French physician and psychologist, highlighted the existence of male hysteria in his famous book Traité Clinique et Therapeutique de l'Hystérie published in 1859 and influenced Jean‐Martin Charcot (1825–1893) and other contemporaries.3 Late in the 19th century, Charcot noted that male hysteria was not rare, but it may go unrecognized even by prominent physicians. He stated: “One can concede that a young and effeminate man might develop hysterical symptoms following emotional stress; however, a strong and vital workman for instance, a railway engineer, fully integrated to the society and never prone to emotional instability should become hysteric seems to be beyond the imagination, and yet it is a fact, one we must get used to.”3 Despite these observations, a reluctance to diagnose male hysteria has been a long‐standing trend among physicians and other health care providers.4

Functional movement disorders (FMDs), previously known as “psychogenic movement disorders,” are among the most frequently recognized FNDs.2, 5 Despite the recognition of FMDs in males, studies comparing clinical and demographic features between genders are lacking. We aimed to define the frequency of FMDs in males among diverse age groups and compare the clinical phenomenology of FMDs and comorbid psychiatric features between genders.

Patients and Methods

We studied a cohort of 196 consecutive patients presenting for evaluation of FMDs to the Parkinson's Disease Center and Movement Disorders Clinic, Baylor College of Medicine (Houston, TX). The diagnosis of FMDs was carried out by a group of movement disorders specialists, based on the “probable” category of the Fahn‐Williams criteria, corresponding to the “clinically established” category of the Gupta and Lang criteria.6, 7 Immediately after the initial evaluation in the clinic, patients were taken to the video studio, where an interview focusing on the mode of onset and events preceding the onset, as well as phenomenology, were recorded. The video was subsequently reviewed to obtain the data relevant to this study, summarized in the tables.

We compared the demographic features, clinical phenomenology, psychiatric comorbidities, and triggering factors between men and women with FMDs. We also included information related to comorbid FNDs such as functional paralysis, functional (psychogenic) seizures, and functional speech and voice disorders. For purposes of this study, physical trauma, physical disease, or surgical procedure was considered when one or more of any of these relevant events occurred within 4 weeks before the onset of FMDs. Psychological trauma or stress was considered when a patient admitted having a high psychological stress burden related to social, family, sexual, economic, or job issues. Additionally, we stratified patients according to the age at onset into three categories: ≤18, 19 to 59, and ≥60 years and compared them with respect to clinical and demographic features. All patients or their legal guardian signed written informed consent for videotaping and publishing in a scientific journal approved by the Baylor College of Medicine Institutional Review Board for Human Research.

Statistical Analysis

We summarized the data by descriptive statistics using means ± standard deviations, range, and percentages. The independent t test was used to compare means between groups. The chi‐square (χ2) test and Fisher's exact test were used to compare proportions. All statistical evaluations were performed using SPSS software (version 22; SPSS, Inc., Chicago, IL). A P value <0.05 was considered significant, whereas a statistical trend was considered with P value between 0.05 and 0.099.

Results

We studied a total of 196 consecutive patients diagnosed with FMDs, 59 (30%) of whom were males. Compared to women, men had an older age at onset (40.5 vs. 34.1 years; P = 0.026) and an older age at evaluation (43.8 vs. 38.1 years; P = 0.041; Table 1).

Table 1.

Clinical and epidemiological differences between men and women with FMDs from the entire cohort

	Men, n = 59 (%)	Women, n = 137 (%)	P Value
Age at onset (years)	40.5 ± 19.9	34.1 ± 17.6	0.026
Age at presentation (years)	43.8 ± 19.3	38.1 ± 17.6	0.041
Duration of symptoms before initial evaluation (years)	3.1 ± 4.3	3.8 ± 4.8	0.368
Phenomenology (FMDs)
Tremor	32 (54.2)	64 (46.7)	0.357
Dystonia	12 (20.3)	65 (47.5)	<0.001
Mobile	10	54	0.983
Fixed	2	11
Myoclonus	9 (15.3)	16 (11.7)	0.491
Gait disorder	26 (44)	41 (30)	0.056
Parkinsonism	7 (11.9)	10 (7.3)	0.298
Tics/stereotypies	9 (15.3)	14 (10.2)	0.315
Hemifacial spasm	2 (3.4)	14 (10.2)	0.156
Chorea/athetosis	1 (1.7)	2 (1.5)	1.000
Phenomenology (other)
Speech/voice disorder	8 (13.6)	24 (17.5)	0.492
Seizures	1 (0.73)	4 (3)	1.000
Paralysis	1 (0.73)	4 (3)	1.000
No. of functional phenomenologies	1.83 ± 0.90	1.94 ± 0.90	0.442
	n = 38	n = 87
Psychiatric comorbidity
Anxiety disorder	15 (25.5)	41 (30)	0.429
Depression	8 (13.6)	27 (19.7)	0.253
Related trauma
Physical	10 (17)	11 (8)	0.060
Psychological	18 (30.5)	53 (38.7)	0.159
Physical disease or surgery	5 (8.5)	15 (11)	0.567

Statistically significant in bold numbers.

When comparing the distribution of functional phenomenology in the whole cohort, females had more frequent functional dystonia than males (n = 65 [47.5%] vs. n = 12 [20.3%]; P < 0.001), without any difference in the proportion of mobile versus fixed dystonia between genders (P = 0.983). There was a trend for a higher frequency of functional gait disorder favoring males (44% vs. 30%; P = 0.056). The relative frequency of functional tremor, myoclonus, parkinsonism, tics, stereotypies, hemifacial spasm, chorea, and other FNDs, such as paralysis, seizures, speech, and voice disorders, did not differ between genders (Table 1).

In our cohort, 125 patients had detailed data regarding psychiatric comorbidities and triggering conditions. Frequency of comorbid anxiety and depression did not differ between genders; however, male patients showed a statistical trend toward a higher prevalence of physical trauma preceding the onset of FMDs; no difference was found between previous psychological stress, physical disease, or recent medical procedure (i.e., surgery; Table 1). When considering patients aged between 18 and 59 years, functional dystonia still favored females (P = 0.001), whereas men had more frequent physical trauma (30.4% vs. 11%; P = 0.047), and women acknowledged psychological trauma more commonly than men (62% vs. 34.7%; P = 0.025; Table 2).

Table 2.

Clinical and epidemiological differences between men and women with FMDs aged between 18 and 59 years

	Men, n = 40 (%)	Women, n = 100 (%)	P Value
Age at onset (years)	41.3 ± 13.7	38.5 ± 11.2	0.275
Age at presentation (years)	44.5 ± 13.4	41.8 ± 12.9	0.170
Duration of symptoms before initial evaluation (years)	3.4 ± 4.8	3.5 ± 3.8	0.814
Phenomenology (FMDs)
Tremor	22 (55)	47 (47)	0.422
Dystonia	7 (17.5)	49 (49)	0.001
Mobile	6	46	0.423
Fixed	1	3
Myoclonus	4 (10)	11 (11)	1.000
Gait disorder	18 (45)	33 (33)	0.183
Parkinsonism	3 (7.5)	9 (9)	1.000
Tics/stereotypies	6 (15)	10 (10)	0.393
Hemifacial spasm	2 (5)	12 (12)	0.350
Chorea/athetosis	1 (2.5)	2 (2)	1.000
Phenomenology (other)
Speech/voice disorder	6 (15)	20 (20)	0.492
Seizures	0 (0)	1 (1)	1.000
Paralysis	1 (2.5)	2 (2)	1.000
No. of functional phenomenologies	1.8 ± 0.8	2.0 ± 0.9	0.179
	n = 23	n = 63
Psychiatric comorbidity
Anxiety disorder	8 (34.7)	28 (44.4)	0.421
Depression	5 (21.8)	19 (30.2)	0.441
Related trauma
Physical	7 (30.4)	7 (11.1)	0.047
Psychological	8 (34.7)	39 (61.9)	0.025

Statistically significant in bold numbers.

Gender Distribution and Phenomenology at the Extremes of Age

When considering only patients aged <18 years (n = 38), males were still under‐represented (n = 10; 26.3%). Age at onset and at presentation did not differ between genders in this age group; however, the distribution of clinical phenomenology was similar, including for functional dystonia (P = 0.461), although males had a higher proportion of functional gait disorder (50% vs. 10.7%; P = 0.019; Table 3). Other clinical variables, including triggering factors and psychiatric comorbidities, did not differ between genders, although a trend for higher prevalence of depression was observed in females at this age group (P = 0.061; Table 3). When analyzing patients aged <14 years (n = 17), males were still under‐represented (n = 3; 17.6%). After plotting age at onset and gender, the proportion of male and female cases did not differ in patients aged ≥50 years (Fig. 1). Furthermore, no differences were found in the phenomenology distribution or psychiatric comorbidities in this group (n = 50; Supporting Information Table S1). No differences were either observed in patients aged ≥60 years (n = 18), where males also represented 50% of cases.

Table 3.

Clinical and epidemiological differences between boys and girls with FMDs aged <18 years

	Boys, n = 10 (%)	Girls, n = 28 (%)	P Value
Age at onset (years)	14.0 ± 2.4	13.50 ± 2.23	0.555
Age at presentation (years)	16.5 ± 4.5	17.8 ± 8.9	0.658
Duration of symptoms before initial evaluation (years)	2.65 ± 3.58	5.1 ± 7.6	0.344
Phenomenology (FMDs)
Tremor	4 (40)	12 (43)	1.000
Dystonia	4 (40)	15 (53.5)	0.461
Myoclonus	3 (30)	4 (14.3)	0.351
Gait disorder	5 (50)	3 (10.7)	0.019
Parkinsonism	2 (20)	1 (3.6)	0.164
Tics/stereotypies	1 (10)	3 (10.7)	1.000
Hemifacial spasm	0 (0)	2 (7.2)	1.000
Chorea/athetosis	0 (0)	0 (0)	1.000
Phenomenology (other)
Speech/voice disorder	2 (20)	1 (3.6)	0.164
Seizures	1 (10)	2 (7.2)	1.000
Paralysis	0 (0)	2 (7.2)	1.000
No. of functional phenomenology	2.00 ± 1.16	1.610 ± 0.875	0.270
Psychiatric comorbidity
Anxiety disorder	5 (50)	9 (32)	0.678
Depression	0 (0)	8 (28.6)	0.061
Related trauma
Physical	2 (20)	4 (14.3)	1.000
Psychological	6 (60)	10 (35.7)	0.405

Statistically significant in bold numbers.

Figure 1.

Gender distribution by every decade of life in this study.

Discussion

Females represent the majority of patients presenting for evaluation in major case series of patients with FMDs.8 It has been argued that this difference might be, at least partially, explained by the fact that these are clinic‐based populations and women tend to access health services more frequently than men, with an odds ratio of 1.5:1.8, 9 This difference is partly explained by cultural and biological factors. In a large study comparing access to medical care in almost 2 million men and 2 million women, the crude consultation rate was 32% lower in men than women; such a lower rate for men persisted even after accounting for reproductive‐related consultations.10 However, consultation rates tend to equalize when similar conditions are compared.10, 11 These findings question the assumption that men are more reluctant to seek medical consultation than women. In a study including 3,781 patients from general neurology clinics in Scotland, there were 1,144 patients with symptoms unexplained by organic disease.12 Among these patients, women were over‐represented for those diagnosed with conversion symptoms, such as functional sensory (53%), nonepileptic attacks/dissociative seizures (73%), and functional weakness, gait, or movement disorder (80%)13; this observation suggests that the higher rate of consultations by women with FMDs may simply reflect the overall higher incidence of this group of disorders in female gender.

In our entire cohort, dystonia was more frequently observed in adult females, but there was no difference in the frequency of dystonia in populations aged <18 years or ≥50 years. Another study has found that functional dystonia, particularly fixed dystonia, is more commonly observed in females than males; that study included 103 patients with fixed dystonia, with a mean age at onset of 29.7 years, and 84% were females.14 In one study, which included 73 patients with FMDs, tremor was predominantly observed in adults, whereas myoclonus was most commonly observed in children.15 In another study, tremor was the most common phenomenology in adults and children with FMDs.16

FMDs also present at the extremes of age: children and the elderly. In a meta‐analysis of 120 children with FMDs reported in six different studies, 33 (27.5%) were males,17, 18, 19 a figure very similar to the one reported in this study (26.3%). Mean age at onset ranged between 11.5 and 14.2 years among studies. There was no difference in specific phenomena between genders in this age group. In a previous study from our clinic population, which included a different set of patients from those in the current study, 12 (28.5%) of 54 children were males, but there was no gender difference in children aged <14 years,20 although in the current study there was a marked female preponderance even in children aged <14 years. The proportion of males and females was equal in patients aged ≥60 years in our study. This contrasts with another study that included 30 patients with FMDs aged ≥60 years in which males represented only 27.3% of cases.21 Interestingly, in a study of 296 patients with “psychogenic nonepileptic seizures” (PNES), those >55 years were more likely to be male (P = 0.029).22 Although PNES are over‐represented in women, men constitute around 30% of cases without major differences in demographic and clinical characteristics.23, 24, 25, 26 Thus, PNES should be considered within the continuum of FMDs, and both are within the spectrum of FNDs.27

There is currently no clear scientific explanation for the differences in gender prevalence favoring females and phenomenology type of FMDs; it can be argued that neurobiological, hormonal, cultural, social, and previous history of psychological or sexual trauma may contribute, although similar gender distribution in patients aged ≥50 years would suggest convergence of neurobiological conditions predisposing to FMDs at this age in both genders. Some researchers have claimed that FNDs are linked to sexual issues in women, including sexual abuse, which may increase their predisposition to FNDs28, 29, 30; however, this may be an oversimplification, considering emerging evidence attributing a complex and multidimensional nature to FNDs.2

Our study has some limitations given that the enrollment was carried out in a tertiary, referral center for movement disorders, which may potentially bias the gender and phenomenology distribution of these patients. For example, it is possible that referring physicians or family members may be reluctant to ask for consultation in our clinic for males affected with FMDs. This suggests the possibility of underdiagnosis of FMDs in males. In one study of 160 consecutive patients with PNES, the family members were 3 times less likely to accept the diagnosis of PNES in men.23 The retrospective assessment of some clinical variables, such as physical and psychological trauma, may also be subject to bias, given that we did not use a standardized method to quantify traumatic life events.31 The frequency of these variables observed in our population, however, is similar to other series. The increased frequency of psychological trauma in females may be attributed to increased probability to admit traumatic events by women or minimize them by men. Finally, the sample size in patients aged ≥60 years was relatively small (n = 18), which may limit the conclusions in this group.

In conclusion, females represented 70% of cases of FMDs in a relatively large cohort of patients with FMDs. Males were older at onset compared to females. Females had a higher frequency of dystonia in middle‐aged patients (between 18 and 59 years), but this gender bias for functional dystonia was lost at the extremes of ages. Functional gait disorders tend to be more frequent in males, particularly in those aged <18 years. Although female gender is overall over‐represented in patients with FMDs, this gender distribution disappears for those aged ≥50 years. The differences for these gender and phenomenology distributions are unclear, but several neurobiological, hormonal, cultural, and social factors may be implicated.

Author Roles

Research articles, etc.: (1) Research Project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript Preparation: A. Writing of the First Draft, B. Review and Critique.

J.F.B.‐C.: 1A, 1B, 1C, 2A, 2B, 3A, 3B

J.J.: 1A, 1B, 2C, 1C, 3B

Disclosures

Ethical Compliance Statement

The authors confirm that patients signed a written informed consent approved by the Baylor College of Medicine IRB for video recording and publication in a scientific journal of all patients included in this study. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflicts of Interest

The authors report no sources of funding and no conflicts of interest.

Financial Disclosures for previous 12 months

Dr. Baizabal‐Carvallo has received royalties from Medlink Neurology; he serves on the editorial board of BMC Neurology. Dr. Jankovic has recieved research/training funding from Allergan, Inc, CHDI Foundation, Dystonia Coalition, F. Hoffmann‐La Roche Ltd, Huntington Study Group, Medtronic Neuromodulation, Merz Pharmaceuticals, Michael J Fox Foundation for Parkinson Research, National Institutes of Health, Neurocrine Biosciences, Parkinson's Foundation, Nuvelution, Parkinson Study Group, Revance Therapeutics, Inc, and Teva Pharmaceutical Industries Ltd; has served as consultant/advisory board for Abide, Lundbeck, Retrophin, Inc‐Parexel, Teva Pharmaceutical Industries Ltd, and Allergan; has served on the editorial boards of Expert Review of Neurotherapeutics, Journal of Parkinson's Disease, Medlink, Neurology in Clinical Practice, The Botulinum Journal, PeerJ, Therapeutic Advances in Neurological Disorders, Neurotherapeutics, Tremor and Other Hyperkinetic Movements, Toxins, and UpToDate; and has received royalties from Cambridge, Elsevier, Future Science Group, Hodder Arnold, Medlink: Neurology, Lippincott Williams and Wilkins, and Wiley‐Blackwell.

Supporting information

Table S1. Clinical and epidemiological differences between men and women with FMDs aged ≥50 years.