Certain general principles common to FMD also apply to FD. Usually, symptoms appear suddenly and are often precipitated by physical and/or emotional events.[26-28, 38-41] There is marked variability in their phenomenology, progression, and duration. Spontaneous, iatrogenic, or life-event–related remissions and recurrences are common. In many cases, the onset age is unusual for the particular phenotype. Also, as with other FMDs, FD co-occurs with additional functional phenomena. Hence, the typical “company” that FD keeps is functional tremor, myoclonus, and effortful nonparkinsonian slowing of movements, but also additional nonorganic neurologic signs and multiple somatizations.[28, 30, 38, 39, 41-44] Suggestibility and placebo or atypical response to medication are commonly observed (see Video 1).[27, 28, 41] However, neither illness duration, symptom severity, nor previous attempted treatments help in discerning functional from organic. Although a positive family history usually denotes organic disorders, FMD may also affect more than one family members. Finally, FD may coexist with organic movement disorders or other neurological illness (functional overlay).[27, 30, 42] In these cases, they usually affect the same or adjacent body parts.[3, 46]
However, in addition to these general characteristics, systematic clinical observations have led to the delineation of three distinct dystonic presentations likely to be functional. These include cranial, fixed, and paroxysmal dystonic phenotypes.
Functional Cranial Dystonia
FD predominantly involving the face occurs in approximately 16% of all FMDs. Females are most commonly affected.[3, 30, 43, 47, 48] Symptoms usually appear between the fourth and sixth decades, but onset in childhood is possible. Symptoms emerge abruptly. The lower face is most commonly affected. Unilateral or asymmetric involvement is common. Symptoms are most often paroxysmal and consist of tonic spasms with brief periods of normal facial muscle activity in between.[30, 43, 47, 48] However, sustained fixed posturing for several days is reported. Unilateral downward lip pulling, which can be reported to be painful with adjacent platysma contractions, is very common (see Video 2, Segment A). In many cases, speech is normal; however, difficulties may be present. In the vast majority of patients, swallowing remains unaffected.
When the eyes are predominantly affected (“functional blepharospasm”), again abrupt and asymmetric symptom onset with constant–tonic–eye closure (see Video 2, Segments B–D) are common.[3, 43, 47] However, patients may also show continuous bilateral eye closure without prominent muscle activity (“psychogenic pseudoptosis” and “hysterical blepharospasm”[51-54]; see Video 2, Segment E). Suggestibility and unusual cues hint toward a functional cause. In asymmetric presentations where intermittent spasms affect the entire side of the face mimicking hemifacial spasm, the lack of synchronicity between lower and upper facial muscles and occasional bilateral tonic contractions of the lower face with unilateral spasm of the upper face are useful diagnostic clues. Typically, spasms are much more prolonged than the very brief electric shock-like spasms of typical hemifacial spasm. Also, the absence of the “other Babinski sign” (synchronous contraction of the orbicularis oculi and frontalis muscles leading to eye closure with ispilateral eyebrow elevation) aids in diagnosis (see Video 2, Segments B–D). As with other FMDs, immediate therapeutic response to botulinum toxin, if present, further contributes in recognizing a functional cause.
Functional Fixed Dystonia
Fixed dystonia (i.e., reduced joint mobility resulting from dystonic posturing) is not a common phenotypic presentation of primary dystonia (including idiopathic and/or inherited forms of dystonia, according to the new dystonia classification). It may, however, be encountered in secondary dystonic conditions in advanced disease stages. It also differs from mobile dystonia, in that it is painful and does not improve to sensory tricks. Patients with fixed dystonia do not exhibit overflow dystonia.[38, 39] Fixed dystonia affects more females and is often elicited by minor traumas and commonly co-occurs with pain, which, in some cases, fulfills criteria for chronic regional pain syndrome type I (CRPS-I).[38, 39, 44] The latter denotes a syndrome consisting of autonomic (e.g., vasomotor, sudomotor, and trophic), sensory (e.g., pain or hyperalgesia), and motor (e.g., decreased range of motion, weakness, and posturing) symptoms. Different from type II CRPS, type I develops in the absence of peripheral nerve injury.
In contrast to primary (and mobile) dystonia, fixed dystonia commonly develops rapidly (overnight or in a few days) after a minor precipitating event.[27, 28, 38, 39] It usually presents as resting dystonia at onset and usually affects the lower limbs,[38, 39] but can also manifest in the hands or neck/shoulders. It typically consists of foot inversion with plantar flexion and curling of toes (see Video 3, Segment A). In the hands, there is typically metacarpo- and/or interphalangeal flexion, mostly of the fourth and fifth fingers, with the thumb least or not functionally affected (see Video 3, Segments B–E). In most cases, pain is a major complaint. For the neck, in the absence of severe trauma-induced musculoskeletal injuries, tonic dystonic posturing with ipsilateral shoulder elevation and prominent pain has been described.[62-65] A disappointing long-term response to local botulinum toxin injections is characteristic, and the term “post-traumatic painful torticollis” has been proposed.[62, 63] Dystonic posturing can spread to both ipsi- and contralateral limbs or may co-occur with other functional motor symptoms. Give-way weakness, functional jerks, and tremor have been noted in affected and nonaffected body parts.[27, 28, 38, 39, 44, 63]
In the largest study to date to assess the features of fixed dystonia in 103 patients (41 of which were prospectively examined), “psychogenic signs” had been documented for 33% of all patients, but were even more common in the prospectively examined group (46%). In fact, 90% of patients of the latter group were found to fulfill different levels of the Fahn and Williams criteria for FD, with 37% (15 of 41 patients) receiving a diagnosis of either documented or clinically established FD. Further, the co-occurrence of affective, somatization, and dissociative disorders was significantly higher for patients with fixed dystonia, when compared to primary dystonia controls. Although pain was a main characteristic in nearly all patients, less than half of the prospectively examined subgroup exhibited cardinal features of CRPS and only 20% fulfilled diagnostic criteria. The presence of CRPS has been shown to be the main predictor of poor outcome for fixed dystonia.
A great controversy surrounds the etiological nature of fixed dystonia with or without CRPS-I. However, for at least a subset of patients presenting with fixed dystonia in the absence of secondary causes, aforementioned syndromic characteristics should prompt the consideration of FD. Spontaneous symptom improvement upon conflict resolution in some cases, good therapeutic effects of multidisciplinary treatment approaches with a particular focus on cognitive-behavioral therapy, as well as immediate dramatic responses to placebo treatments further support this notion.[27, 28, 39, 44, 56]
The management of the severe pain reported by patients with fixed dystonia, which is exacerbated upon tactile stimulation or light movement, is challenging.[39, 44] The severity of symptoms and uncertainty regarding the diagnosis often lead to invasive procedures, including limb amputation, however with poor outcome. Of note, seeking of limb amputation is only encountered extremely rarely in other dystonic conditions,[67, 68] but has been reported in CRPS-I.[69-71] Thus, the possibility has been raised that patients with fixed dystonia and CRPS-I who seek limb amputation might have deficits in their body schema perception as part of the body identity integrity disorder spectrum.
Functional Paroxysmal Dystonia
Although paroxysmal FD has been well recognized and constitutes common clinical presentation, its characteristics had only been rarely highlighted in recent literature.[72-75] When it predominantly affects the extremities and/or trunk and on a background of unrevealing neurophysiologic, imaging, and laboratory examinations, its differentiation from other paroxysmal disorders, in particular, the primary paroxysmal dyskinesias, may be challenging.[41, 72]
Fahn and Williams described 7 of 21 FD patients with paroxysmal symptoms, 4 of which had documented and 3 established FD. They pointed out the high prevalence of FD in patients with paroxysmal dystonia and subsequently indicated that variable and inconsistent nonorganic startle responses often trigger paroxysmal episodes of FD (see Video 4, Segment A). Increased suggestibility and the unusual combination of additional abnormal movements in addition to dystonic posturing, which are not observed in classic presentations of primary paroxysmal dyskinesias, typify these patients (see Video 4, Segment B).
However, it was recent advances in genetic characterization of the three main primary forms of paroxysmal dyskinesias (paroxysmal kinesigenic dyskinesia [PKD], paroxysmal nonkinesigenic dyskinesia [PNKD], and paroxysmal exercised-induced dyskinesia [PED]) that have allowed their typical phenotypic characteristics to be recognized and distinguished from atypical forms.[76-88] We recently reported on the characteristics of a large case series of patients with functional paroxysmal movement disorders, including patients with functional paroxysmal dystonia, and compared them to proposed diagnostic criteria of PKD, PNKD, and PED. In this regard, one of the most important pointers is that typically all three primary forms present very early in life, during the first or second decade. However, in functional paroxysmal dystonia, symptoms usually appear much later on.[27, 28, 30, 41]
Another important aspect is the great variability between attacks in terms of duration and phenomenology. Although in primary paroxysmal dyskinesias between-subject variability exists in attack duration, great intraindividual variability is uncommon. For example, in PKD, attacks typically last less than 1 minute and only rarely do they vary by more than a few minutes in a single patient.[76, 83, 89] In contrast, attacks in functional paroxysmal dystonia may differ greatly in duration in individual patients (e.g., between seconds and hours/days). Furthermore, in functional paroxysmal disorders, the predominant movement disorder may shift in nature between attacks. For example, paroxysmal tremor has been noted to occur at times in patients who have attacks of dystonia at other times, strongly hinting at nonorganicity. A complete list of diagnostic red flags hinting toward a functional disorder is given in Table 3.
Table 3. Clinical hints of functional paroxysmal dystonia adapted from Ganos et al.
|Adult age of onset|
|Presence of paroxysmal tremor|
|High phenomenological variability of episodes|
|Precipitation of attacks or increase in symptom severity during examination|
|Atypical and variable duration of attacks|
|Presence of multiple atypical triggers|
|Altered level of responsiveness|
|Presence of atypical precipitating factors|
|Presence of unusual relieving maneuvers|
|Additional psychogenic physical signs and/or medically unexplained somatic symptoms|
|Atypical response to medication|
Neurophysiology as an Aid for Diagnosis of Functional Dystonia
A number of different electrophysiological techniques have been applied to patients with organic and presumed FD. These have shown some similarities, but also differences. From the clinical perspective, it would be of great use to have an electrophysiological test that reliably distinguished between organic and FD. However, despite the work that has been done in this area to date, there are no sufficiently robust tests available that could be used to provide what Gupta and Lang have proposed as a “laboratory-supported” level of diagnostic certainty for functional dystonia.
The R2 component of the blink reflex recovery cycle has been found to be abnormally enhanced in patients with organic blepharospasm. This differs from patients with atypical (or functional) blepharospasm, where it was found to be normal, and separated patients with functional and organic blepharospasm fairly successfully on an individual patient basis. One study has provided limited evidence that the reduction in postexcitatory inhibition after transcranial magnetic stimulation in the affected facial side in patients with hemifacial spasm during spasms and the subsequent prolongation after spasms is not observed in patients with functional spasms and healthy controls, but this awaits confirmation in a larger group of patients.
Other electrophysiological measures, including cortical and spinal cord inhibition (short intracortical inhibition [SICI] and reciprocal inhibition), assessments of associative plasticity, and sensory temporal discrimination, have been performed in patients with organic and fixed dystonia.[92-95] Similarities and differences have been found, but such data are hard to interpret from a pathophysiological point of view and do not as yet form a viable basis for a clinical diagnostic test. Measures such as SICI are vulnerable to interference from the effects of attention toward the limb as well as by the underlying personality disorder.[96, 97] Temporal discrimination testing relies on self-report, and therefore it is difficult to be certain that the abnormalities reported in fixed dystonia are caused by the same underlying mechanism as the abnormalities reported in organic dystonia. In any event, the intraindividual variability of such measures, even in patients with organic dystonia, as well as the technical demands of some of the tests, makes it unlikely that they will be useful as diagnostic measures.