Miguel Schwartz

Antipsychotic-Induced Rabbit Syndrome Epidemiology, Management and Pathophysiology

Rabbit syndrome is an antipsychotic-induced rhythmic motion of the mouth/lips, resembling the chewing movements of a rabbit. The movement consists of a vertical-only motion, at about 5Hz, with no involvement of the tongue. Usually, the involuntary movements associated with rabbit syndrome appear after a long period (in most cases months or years) of antipsychotic treatment; however, a few patients with the syndrome have had treatment histories with no antipsychotic involvement. The reported prevalence of rabbit syndrome ranges from 2.3 to 4.4% of patients treated with typical antipsychotics. There have been isolated reports of rabbit syndrome in patients treated with the atypical agents risperidone and clozapine.Patients with rabbit syndrome are most often misdiagnosed as having oral tardive dyskinesia. In such cases the key for correct diagnosis is the involvement of tardive tongue movements, which does not occur in rabbit syndrome.The treatment of rabbit syndrome is empirical, reflecting poor understanding of its neuropathology. The first step is to reduce the amount of antipsychotic treatment as much as possible. However, since, in most cases, full withdrawal of antipsychotic treatment is impossible, the syndrome cannot be completely abolished without additional measures. The next stage of treatment involves specific drugs that aim to control the syndrome. Anticholinergic drugs are the best known treatment. Rabbit syndrome does not respond to treatment with levodopa or dopamine agonists.The most striking aspect of this syndrome is its specificity. Rabbit syndrome affects only the buccal region, and within this area it involves a highly stereotyped involuntary movement. This immediately focuses attention on the basal ganglia, in particular the substantia nigra pars reticulata, which is also implicated in oral dyskinesia. Continuing neurophysiological and pharmacological research of the basal ganglia holds the key to better understanding and treatment of this syndrome in the coming years.

Visuomotor Performance in Patients With Essential Tremor

Essential tremor (ET) is the most prevalent extrapyramidal disorder, yet its diagnosis is still controversial. This article introduces new findings that pertain to this diagnostic problem. Twenty‐three patients with ET were studied. Patients with parkinsonism, cerebellar signs, severe head injury, or those under neuroleptic medication were excluded. Twenty‐five normal subjects served as control subjects. Visuomotor tests involving tracking and tracing along three different paths with both the right and left hands, were used. Performance was assessed by measuring test duration, directional error, the proportion of the cumulative test time during which directional error exceeded half the maximal possible level (PT50%), the mean distance from the model path, the velocity of the hand movement, and the number of tracking interruptions. In 15 of 23 patients performance was the same as in the control subjects. These patients were defined as having a “simple condition” of ET (ETs). Considerable visuomotor impairment was found in eight patients who were regarded as having a “complex condition” of ET (ETc). Patients with ETc had significantly lower tracking speed, more tracking interruptions, longer test duration, greater directional error, greater PT50%, and greater distance from path than patients with ETs or control subjects. Most patients with ET appear to have normal visuomotor capabilities (ETs) but some display significant visuomotor disturbances (ETc). Considering the presence of similar impairments in patients with early Parkinsons disease and the increased prevalence of parkinsonism in patients with ET, it is possible that preclinical parkinsonism exists in patients with ETc. Further follow up of patients with ETc is necessary to verify this possibility.

Adaptation to cyclic stance perturbations in Parkinson's disease depends on postural demands

The postural reactions of 10 moderate PD patients and 10 age matched controls were studied during stance on a sinusoidally back and forth moving platform during 5 blocks of 10, 1-min trials. Free stance was followed by weight bearing, lowering or raising the center of gravity (COG) by 10%. Next, a book was balanced on the head and finally, forward inclination was constrained. Normal stance strategy, including predictive muscle responses was found during free stance. Modifying COG height caused little response changes. Stance strategy became abnormal when head trajectory or forward inclination was restricted, indicating that ability to generate a nonstandard multi-joint stance strategy, rather than production of adequate stabilizing forces, is impaired in moderate, medicated PD patients.

Sensor Array for Detection of Early Stage Parkinson’s Disease before Medication

Early diagnosis of Parkinsons disease (PD) is important because it affects the choice of therapy and is subject to a relatively high degree of error. In addition, early detection of PD can potentially enable the start of neuroprotective therapy before extensive loss of dopaminergic neurons of the substantia nigra occurs. However, until now, studies for early detection of PD using volatile biomarkers sampled only treated and medicated patients. Therefore, there is a great need to evaluate untreated patients for establishing a real world screening and diagnostic technology. Here we describe for the first time a clinical trial to distinguish between de novo PD and control subjects using an electronic system for detection of volatile molecules in exhaled breath (sensor array). We further determine for the first time the association to other common tests for PD diagnostics as smell, ultrasound, and nonmotor symptoms. The test group consisted of 29 PD patients after initial diagnosis by an experienced neurologist, compared with 19 control subjects of similar age. The sensitivity, specificity, and accuracy values of the sensor array to detect PD from controls were 79%, 84%, and 81% respectively, in comparison with midbrain ultrasonography (93%, 90%, 92%) and smell detection (62%, 89%, 73%). The results confirm previous data showing the potential of sensor arrays to detect PD.

Visuo-motor coordination is normal in patients with major depression

Depression and Parkinsons disease (PD) are strongly associated with each other. Similarly, deficient visuo-motor coordination (VMC) accompanies PD from its earliest clinical stages. This double association suggests that a VMC dysfunction would be found in patients with major depression. Previous reports are ambiguous on this matter. Therefore, the present study was undertaken in order to determine whether MD patients pass or fail a VMC test on which PD patients are known to be deficient.Sixty-five MD patients were tested. Fifty-four (83%) had normal VMC. VMC was found to be independent of age, disease duration, severity of depression, or treatment. A deficit was found in 12 patients (17%). In this group too, VMC capabilities did not correlate with depression, or its treatment.These results negate an effect of depression, its accompanying frontal cortical changes, or its treatment on VMC. We propose that abnormal VMC in depression indicates coexisting illness, including possible preclinical PD.