Discussion

FMDs are heterogeneous disturbances of motor function that are not explained by organic conditions and may occur in association with underlying psychiatric disease.^{Reference Schwingenschuh, Pont-Sunyer and Surtees12} FMD poses a great challenge for clinicians in diagnosis and management.

In our study, 39 children with documented and clinically established FMD were evaluated. The most common type of FMD observed was myoclonus, tremor, and dystonia. The exact prevalence or frequency of pediatric FMD varies between 2% and 3% of children attending the movement disorders clinic.^{Reference Ferrara and Jankovic2,Reference Schwingenschuh, Pont-Sunyer and Surtees12,Reference Fernández-Alvarez13} In a study involving 2280 children with neurological disorders, psychogenic etiology was observed in 6.4%.^{Reference Thomas14}

In our study, FMD was more common in boys, which is similar to the previous two studies from India.^{Reference Kamble, Prashantha and Jha3,Reference Pandey and Koul15} However, some previous studies have shown the higher prevalence in girls.^{Reference Ferrara and Jankovic2,Reference Schwingenschuh, Pont-Sunyer and Surtees12,Reference Ahmed, Martinez and Yee16,Reference Canavese, Ciano and Zibordi17} In another study from our institute, about 48% of patients with the then-existing diagnostic category of hysteria were girls.^{Reference Srinath, Bharat and Girimaji18} The reason for predominance of FMD in boys is not clear, but it may be due to sociocultural practices prevailing in the Indian community wherein medical attention is sought more often and earlier for the boys than girls. Indian society is mainly patriarchal.^{Reference Prusty and Kumar19} There is a preference for a son in most of the Indian families and there is discrimination against girls especially in providing education and medical care.^{Reference Arnold, Choe and Roy20}

In our study, majority of the children belonged to low-to-middle socioeconomic strata. In India, patients from low-to-middle socioeconomic populations more often visit government hospitals, like ours. However, to the best of our knowledge, there is no published literature from India on the prevalence of pediatric FMD based on socioeconomic status.

Abrupt onset of symptoms is one indicator toward FMD, which was seen in 69.2% of our cohort. In a study of 54 children, approximately 90% of children presented with an abrupt onset.^{Reference Ferrara and Jankovic2} Many other studies have also reported a preponderance of abrupt onset of illness.^{Reference Canavese, Ciano and Zibordi17} In addition, antecedent illness is commonly seen in these patients. In our study, nearly a third of the children had an antecedent illness which is similar to the other studies.^{Reference Kamble, Prashantha and Jha3,Reference Canavese, Ciano and Zibordi17}

History of precipitating factors needs to be enquired in patients suspected of FMD. Most of the studies have reported precipitating factors ranging from 47.9% to 83.7% in adults.^{Reference Ertan, Uluduz and Ozekmekçi21,Reference Kim, Pakiam and Lang22} The various precipitating factors identified in these studies include physical injury, psychological insult, flu-like illness, death of a relative, poverty, family, or social stress.^{Reference Ertan, Uluduz and Ozekmekçi21–Reference Thomas, Vuong and Jankovic23}

In a study involving 38 children, significant stressors were identified in 27 that included academic difficulties in school, punitive parent, parental discord, financial difficulties, increasing workload, and sibling rivalry.^{Reference Srinath, Bharat and Girimaji18} Traumatic experience (physical or psychological) and emotional factors in the childhood have a significant impact on the pathogenesis of FMD.

Myoclonus followed by tremor and dystonia were the common phenomenologies observed in our study. However, tremor^{Reference Ferrara and Jankovic2,Reference Canavese, Ciano and Zibordi17,Reference Srinath, Bharat and Girimaji18} and dystonia^{Reference Schwingenschuh, Pont-Sunyer and Surtees12,Reference Faust and Soman24} have been the most common FMD in other studies.

Detailed psychiatry evaluation is necessary for diagnosis and treatment of FMD. The various psychiatric comorbidities that have been associated with FMD include obsessive-compulsive disorders, depression, and anxiety.^{Reference Voon, Brezing and Gallea25}

Clinically, it is challenging to diagnose FMD. However, some cues that may be useful for diagnosis can be categorized as historical (abrupt onset, static course, psychiatric comorbidity, precipitating factors, presence of multiple somatizations, pending litigation, etc.), clinical (incongruence, inconsistency, distractibility, variability, entrainability, fluctuating course, suggestibility/modulation, episodic occurrence with complete or incomplete remissions, spontaneous remissions, and additional movement disorders), and treatment related (response to psychotherapy, placebo).^{Reference Kim, Pakiam and Lang22} Electrophysiological methods such as surface EMG recording for tremors and BP in myoclonus may be helpful in determining the functional basis for the movement disorders.^{Reference Kamble, Prashantha and Jha3}

Recent neuroimaging studies have implicated abnormal emotional processing, sense of agency, and top-down regulation from frontal areas as important pathophysiological components in FMD.^{Reference Voon, Brezing and Gallea25} Abnormal regional brain activations and functional connectivity have been demonstrated using functional MRI and positron emission tomography (PET).^{Reference Stone, Zeman and Simonotto26} Abnormal connectivity is found in right caudate, amygdala, prefrontal, and sensorimotor regions in patients with FMD with over 68% sensitivity and specificity.^{Reference Wegrzyk, Kebets and Richiardi27} In addition to the abnormal activation of supplementary motor area (SMA), patients with functional tremors and dystonia have abnormal activation in the right middle temporal gyrus or right temporoparietal junction.^{Reference Espay, Maloney and Vannest28} The cingulate cortex has been implicated in self-awareness, self-monitoring, and active motor inhibition.^{Reference Aybek, Nicholson and O’Daly29} In patients with functional tremors and dystonia, there is abnormal activation of the cingulate cortex.^{Reference Hedera30} In future, these advanced imaging techniques may be useful in the diagnosis of FMD. Currently, these studies have been done only in adults. There are no such studies in pediatric FMD.

In our study, 56.4% of children had complete resolution of symptoms, and in 11.1%, there was a partial improvement and 13.9% showed no improvement at all, which may be due to non-acceptance of functional nature of the disease by parents/patients. There was no child with a worsening of symptoms. Studies have reported response rates ranging from 5% to 57%.^{Reference Thomas, Vuong and Jankovic23,Reference Hedera30–Reference Munhoz, Zavala and Becker33} Similar good outcome has been observed in previous studies from India.^{Reference Pandey and Koul15} In another study, the outcome was not described due to lack of follow-up which is a problem with patients with FMD.^{Reference Ferrara and Jankovic2} In a study by Schwingenschuh et al., 47% improved completely, 33% improved substantially, and 20% remained chronically and severely disabled.^{Reference Schwingenschuh, Pont-Sunyer and Surtees12} A summary of the previous and present studies is shown in Table 3.

Table 3: Spectrum of PMD phenomenology in other studies