Out of 39 referred patients retrieved from the movement disorders database, five were excluded (three for inconclusive clinical or neurophysiological documentation). One patient was diagnosed with belly dancer's dyskinesia and was excluded. In the remaining 35 patients (18 men), characteristics suggestive of a psychogenic origin of the axial jerks were present. Median age was 47 years (range 17–83 years). Mean duration of symptoms was 43 months (median 20, range 1–360 months). In eight cases, the diagnosis of clinically definite psychogenic axial jerks was made. These patients had no additional electrophysiological investigations, or refused them (n = 2). One patient was diagnosed with secondary PSM (ciprofloxacin) (published previously) . In the other 26 patients electrophysiological investigations supported a probable psychogenic origin.
Twenty-five patients had jerks when sitting and 24 of them also when lying down. In ten of these patients, jerks were more severe when lying down. Ten patients had axial flexion jerks when walking, one of them only had jerks when active (walking, knee buckling) and one only after (minimal) physical exercise. In four patients, facial musculature was involved in the jerks. During sleep none of our patients reported axial jerks, although this was not objectified by polysomnography. None of the patients had a history of restless legs syndrome (RLS) either nor periodic limb movements (PLMD) during sleep. Jerks were stimulus sensitive in seven patients.
Clinical clues suggestive of psychogenesis
Onset of jerks was acute in 26 cases; six patients had paroxysmal jerk attacks. One patient had had a spontaneous remission and one patient had already had spontaneous long symptom free periods. Fifteen patients had a psychiatric history. Two were diagnosed with bipolar disorder (once with a psychotic episode), three with depression, one patient had a history of sexual harassment and two others had been diagnosed with conversion disorder previously from other symptoms (psychogenic tremor and periodic weakness of legs with concomitant speech disturbances). Fourteen patients had multiple somatizations previously. Four of these patients had a history of previously unexplained neurological symptoms. Two of these patients still had subjective impaired vision, impaired coordination, weakness, blackouts and transient sensory deficits. Ten patients appeared emotionally disturbed at time of visit, and three of them had obvious severe psychiatric disturbances. During examination, 19 patients had clinically inconsistent muscle involvement and 28 had a variable pattern of jerks. Distractibility was noted in nine patients.
Fifteen patients had premonitory sensations, and 12 were able to temporarily suppress the jerks. Two patients had urge prior to jerk onset. Two other patients reported rebound after suppression and the same patients felt relieved after the jerks. None of these patients had had a history of motor or vocal tics.
Imaging and laboratory testing
In 27 patients a CT and MRI scan of the head and spinal cord revealed no abnormalities. Two patients refused imaging, and others (n = 5) were unable to lay still. CSF and laboratory testing were normal.
On polymyography (27 cases, one patient refused recordings), 15 patients showed inconsistencies, both in (order of) muscles involved, propagation of the muscle contraction (‘marche’) and duration of jerks. Frequency of jerks varied from once per day to once per 10 s. Some of our patients had ‘bouts’ or flurries of jerks. In 12 patients, a consistent pattern, defined as a consistent first muscle or topography was detected. Only six of them also had a rostral and caudal muscle spread on polymyography typical of PSM. More details on polymyography findings are listed in Table 2. In 17 patients, jerk-locked back averaging was performed. Nine patients with a consistent polymyography had a BP preceding their axial jerks (see Table 2). The three remaining patients with a consistent pattern of jerks did not exhibit a BP. Investigations and analysis were difficult in two patients as, in one of them, jerks were preceded by eye blinking and in the other patient, facial musculature contraction with eye blinking prior to the onset of axial jerks was noted. In none of the patients with an inconsistent pattern on polymyography (n = 5) was a BP found (see Table 2). Figures 1 and 2 display a BP preceding a consistent pattern of jerks and an example of an inconsistent polymyography. Additional SSEP recordings were performed in five patients, none of whom showed giant SSEPs.
Illustrative case report
A 62 year old female with a 1 year history of jerking of the trunk and limbs presented to our clinic for a second opinion. Her medical history consisted of a bipolar disorder, once accompanied by psychosis. Her current medication consisted of lithium, clonazepam and temazepam. Family history included a brother with epilepsy.
The truncal jerks had started acutely 30 min after coloring her hair, which subsequently lead the patient to try to prosecute the producing company. The pattern of jerks changed over time and jerks mainly appeared while lying supine. During the attacks she felt panic and could have unbalanced (not ataxic) walking afterwards. Jerks were accompanied by a premonitory sensory warning and she was able to suppress them, but no rebound occurred. During examination the jerks had a changing pattern and were distractible. Electrophysiology was not performed. Diagnosis of clinically definite psychogenic axial jerks was made, although influence of lithium could not be excluded. The patient was contacted via the telephone after 7 months. She had been treated by a psychiatrist and physiotherapist and had experienced a sudden remission while continuing lithium (unaltered dosage). A video can be found in the Supplementary Material.
Average time from discharge was 40 months (median 23 months, range: 3–104). Thirty out of 33 (one lost to follow-up, one refused participation) patients still had jerks (91%), but most of them to a lesser extent. The patients with continuing complaints rated it 8 out of 10 (SD: 1.4) for severity in the past when seen in the outpatient clinic, and 5 (SD: 1.7) at the time of the telephone call. Written consent of the patients was obtained to contact all GPs and their assessment concurred with the patients account. Moreover, none of the patients had received an alternative diagnosis (by another specialist or neurologist) that could explain the axial jerks.
An overview of clinical work-up and final diagnoses of our case series is provided in Fig. 3. Results are summarized in Tables 1 and 2.