"On" state freezing of gait in Parkinson disease: a paradoxical levodopa-induced complication

OBJECTIVE

To describe the phenotype of levodopa-induced "on" freezing of gait (FOG) in Parkinson disease (PD).

METHODS

We present a diagnostic approach to separate "on" FOG (deterioration during the "on state") from other FOG forms. Four patients with PD with suspected "on" FOG were examined in the "off state" (>12 hours after last medication intake), "on state" (peak effect of usual medication), and "supra-on" state (after intake of at least twice the usual dose).

RESULTS

Patients showed clear "on" FOG, which worsened in a dose-dependent fashion from the "on" to the "supra-on" state. Two patients also demonstrated FOG during the "off state," of lesser magnitude than during "on." In addition, levodopa produced motor blocks in hand and feet movements, while other parkinsonian features improved. None of the patients had cognitive impairment or a predating "off" FOG.

CONCLUSIONS

True "on" FOG exists as a rare phenotype in PD, unassociated with cognitive impairment or a predating "off" FOG. Distinguishing the different FOG subtypes requires a comprehensive motor assessment in at least 3 medication states.

Walking patterns in Parkinson's disease with and without freezing of gait

The pathophysiology underlying freezing of gait (FOG) in Parkinson's disease remains incompletely understood. Patients with FOG ("freezers") have a higher temporal variability and asymmetry of strides compared to patients without FOG ("non-freezers"). We aimed to extend this view, by assessing spatial variability and asymmetry of steps and interlimb coordination between the upper and lower limbs during gait. Twelve freezers, 15 non-freezers, and 15 age-matched controls were instructed to walk overground and on a treadmill. Kinematic data were recorded with a motion analysis system. Both freezers and non-freezers showed an increased spatial variability of leg movements compared to controls. In addition, both patient groups had a deficit in interlimb coordination, not only between ipsilateral arms and legs, but also between diagonally positioned limbs. The only difference between freezers and non-freezers was a decreased step length during treadmill walking. We conclude that parkinsonian gait-regardless of FOG-is irregular, not only in the legs, but also with respect to interlimb coordination between the arms and legs. FOG is reflected by abnormal treadmill walking, presumably because this provides a greater challenge to the defective supraspinal control than overground walking, hampering the ability of freezers to increase their stride length when necessary.

Assessing the interplay between cognition and gait in the clinical setting

In this review, we outline how the influence of cognitive processes on gait or balance can be appreciated in a clinical setting. Careful history taking of the patient or direct carer provides information about multiple task problems in daily life and the presence of cognitive impairment, depression or fear of falling. Physical examination may reveal abnormalities such as an inappropriately high walking speed or an inability to handle secondary tasks while walking. Assessment of frontal executive function helps to understand the nature of these multiple task problems and to detect "risky" behaviour caused by frontal disinhibition. Examples of clinically useable techniques include pressure-sensitive insoles or an electronic walkway (to record strides) or accelerometers (to measure body motion while walking). Combining these assessments may lead to a better appreciation of the fascinating but complex interplay between cognition and gait.

[Gait disorders due to neurological conditions]

Gait disorders are seen frequently and often have a neurological cause. The clinical management of patients presenting with a gait disorder is often complicated due to the large number of diseases that can cause a gait disorder and to the difficulties in interpreting a specific gait disorder properly. In addition, the currently available classification systems are confusing. Gait disorders can be classified into the following categories: antalgic, paretic-hypotonic, spastic, vestibular, ataxic, hypokinetic-rigid, cautious, or functional. A correct interpretation of the gait disorder is important as this determines the diseases to be considered, the auxilliary investigations that have to be carried out, and the selection of rational therapeutic options.

Beck Depression Inventory is a useful screening tool for major depressive disorder in Gilles de la Tourette syndrome

This study determined the prevalence of and factors associated with comorbid major depressive disorder (MDD) in patients with Gilles de la Tourette syndrome (GTS). How a simple self-report instrument, the Beck Depression Inventory (BDI), correlates with clinical assessment of comorbid MDD in this population was assessed. In a continuous sample of 114 adult patients with GTS, assessed clinically using the Diagnostic and Statistical Manual of Mental Disorders-IV criteria, 26 (23%) patients met criteria for MDD; more severe tics as measured with the Yale Global Tic Severity Scale, conduct disorder in childhood or higher age at the time of assessment were associated with MDD. The BDI score had a high negative predictive value for diagnosis of MDD, but a low positive predictive value. Using the BDI as a screening tool for comorbid MDD in patients with GTS is suggested.

Subthreshold rTMS over pre-motor cortex has no effect on tics in patients with Gilles de la Tourette syndrome

OBJECTIVE

A previous study showed no effect of 1Hz repetitive transcranial magnetic stimulation (rTMS) on tics in Gilles de la Tourette Syndrome (GTS). We modified the rTMS protocol in order to investigate some of the possible methodological reasons for the negative outcome in that study.

METHODS

In a single blinded placebo-controlled cross-over study in five GTS patients without obsessive compulsive disorder we probed whether longer trains (1800 stimuli) of 1 Hz pre-motor cortex rTMS at 80% of active motor threshold and application to both hemispheres can improve tics in GTS. This was measured with the Yale Global Tic severity rating scale, the MOVES self-rating scale and video analysis.

RESULTS

We found no significant effect of either left pre-motor cortex stimulation alone, or left pre-motor followed by right pre-motor cortex stimulation.

CONCLUSIONS

These results suggest that the rTMS protocol used in this study is not useful for the treatment of tics in GTS.

SIGNIFICANCE

rTMS protocols need to be modified substantially in order to explore their potential for the treatment of tics in GTS.

[Repetitive transcranial magnetic stimulation in depression; stimulation of the brain in order to cure the psyche]

Transcranial magnetic stimulation (TMS) is a non-invasive approach to briefly stimulate or inhibit cortical brain areas. A novel approach entails the delivery of repetitive TMS pulses (rTMS) at a fixed frequency. In rTMS cortical activity is altered beyond the period of actual stimulation. The changes occur locally as well as at a distance in functionally connected brain areas. These features render rTMS a suitable tool to study normal brain functions and the pathophysiology of brain diseases. Furthermore, it is expected that rTMS could be used as a novel therapy for neurological or psychiatric diseases characterised by abnormal cortical activation. This possibility has been studied mostly in patients suffering from depression, where rTMS has been used to restore normal activity in the hypoactive prefrontal cortex. Despite statistically significant therapeutic effects in small sized trials, the clinical implications are still limited.

The variability of intracortical inhibition and facilitation

OBJECTIVE

To assess the variability of transcranial magnetic stimulation paired pulse measurements of cortical excitability between subjects, between sessions and within subjects within sessions.

METHODS

In experiment 1, intracortical inhibition and facilitation were assessed with a fixed conditioning stimulus intensity (CSI) of 80% of active motor threshold (AMT) whereas in experiment 2, the effect of different CSIs (60-110% of AMT) was investigated.

RESULTS

Experiment 1 revealed that subjects differed significantly in the degree of inhibition and facilitation. Between sessions the variability was substantial as predicted by high within session variability. Experiment 2 allowed determination of individual thresholds for inhibition and facilitation. These thresholds were the best predictor of the amount of inhibition or facilitation at a given CSI. Across subjects we observed a high correlation of the threshold for inhibition (expressed in terms of maximum stimulator output) with AMT (r=0.93). Results for facilitation were more variable.

CONCLUSIONS

The variability was high if a single CSI was used to compare the percent intracortical inhibition or facilitation between subjects, or between sessions. Much less variable was the threshold for intracortical inhibition/facilitation, which was highly correlated to AMT. We suggest that the ratio of CSI:AMT is a robust and useful additional measure of the integrity of neuronal circuits underlying intracortical inhibition/facilitation.