Bell's palsy-induced blepharospasm relieved by passive eyelid closure and responsive to apomorphine

Second hit hypothesis in dystonia: Dysfunctional cross talk between neuroplasticity and environment?

One of the great mysteries in dystonia pathophysiology is the role of environmental factors in disease onset and development. Progress has been made in defining the genetic components of dystonic syndromes, still the mechanisms behind the discrepant relationship between dystonic genotype and phenotype remain largely unclear. Within this review, the preclinical and clinical evidence for environmental stressors as disease modifiers in dystonia pathogenesis are summarized and critically evaluated. The potential role of extragenetic factors is discussed in monogenic as well as adult-onset isolated dystonia. The available clinical evidence for a "second hit" is analyzed in light of the reduced penetrance of monogenic dystonic syndromes and put into context with evidence from animal and cellular models. The contradictory studies on adult-onset dystonia are discussed in detail and backed up by evidence from animal models. Taken together, there is clear evidence of a gene-environment interaction in dystonia, which should be considered in the continued quest to unravel dystonia pathophysiology.

Changes in brainstem excitatory and inhibitory pathways in dry eye syndrome

BACKGROUND

We hypothesized that there may be changes in sensory integration pathways in patients with dry eye. To confront this issue, we analyzed blink reflex (BR), prepulse modulation (PPM) of BR, and excitability recovery of BR to paired stimuli in 17 experimental subjects with dry eye syndrome.

METHOD

We included 17 experimental subjects, 8 with primary and 9 with secondary, dry eye syndrome. We also examined a control group of 14 age and gender matched control subjects. After clinical evaluation, we recorded BR, PPM of BR (at 50 and 100 ms intervals) and BR percentage recovery to paired stimulation (at 300 and 500 ms intervals).

RESULTS

None of the patients had any spasm activity. Experimental subjects had significantly larger R2 and R2c AUCs, significantly greater excitability recovery at 300 ms interval and significantly reduced R2 and R2c prepulse inhibition, in comparison to control subjects. Experimental subjects with primary dry eye syndrome had higher number of spontaneous blinks than experimental subjects with secondary dry eye syndrome (54.0 ± 10.3 for primary dry eye and 43.5 ± 13.3 secondary dry eye).

CONCLUSION

Our results are compatible with increased excitability and abnormalities in sensorimotor integration in blink reflex circuits of patients with dry eye. This suggests the development of adaptive changes in brainstem synaptic activity, aimed at facilitation of blinking in the context of increased sensory input from corneal irritation.

A Dynamic Circuit Hypothesis for the Pathogenesis of Blepharospasm

Blepharospasm (sometimes called “benign essential blepharospasm,” BEB) is one of the most common focal dystonias. It involves involuntary eyelid spasms, eye closure, and increased blinking. Despite the success of botulinum toxin injections and, in some cases, pharmacologic or surgical interventions, BEB treatments are not completely efficacious and only symptomatic. We could develop principled strategies for preventing and reversing the disease if we knew the pathogenesis of primary BEB. The objective of this study was to develop a conceptual framework and dynamic circuit hypothesis for the pathogenesis of BEB. The framework extends our overarching theory for the multifactorial pathogenesis of focal dystonias (Peterson et al., 2010) to incorporate a two-hit rodent model specifically of BEB (Schicatano et al., 1997). We incorporate in the framework three features critical to cranial motor control: (1) the joint influence of motor cortical regions and direct descending projections from one of the basal ganglia output nuclei, the substantia nigra pars reticulata, on brainstem motor nuclei, (2) nested loops composed of the trigeminal blink reflex arc and the long sensorimotor loop from trigeminal nucleus through thalamus to somatosensory cortex back through basal ganglia to the same brainstem nuclei modulating the reflex arc, and (3) abnormalities in the basal ganglia dopamine system that provide a sensorimotor learning substrate which, when combined with patterns of increased blinking, leads to abnormal sensorimotor mappings manifest as BEB. The framework explains experimental data on the trigeminal reflex blink excitability (TRBE) from Schicatano et al. and makes predictions that can be tested in new experimental animal models based on emerging genetics in dystonia, including the recently characterized striatal-specific D1R dopamine transduction alterations caused by the GNAL mutation. More broadly, the model will provide a guide for future efforts to mechanistically link multiple factors in the pathogenesis of BEB and facilitate simulations of how exogenous manipulations of the pathogenic factors could ultimately be used to prevent and reverse the disorder.

Blink reflex studies in postparalytic facial syndrome and blepharospasm: trigeminal and extratrigeminal somatosensory stimulation

PURPOSE

The somatosensory-evoked blink reflex (SBR) is one of the release phenomena of blink reflex, possibly resulting from increased excitability of brainstem reticular formation.

METHODS

The authors investigated trigeminal blink responses and SBR in 26 patients with postparalytic facial syndrome (PFS) with synkinesia, 18 patients with essential blepharospasm, and 36 healthy volunteers (control participants).

RESULTS

Trigeminal blink reflex responses were elicited in all participants, whereas SBRs were elicited in 44.4% of control participants, 38.9% of patients with essential blepharospasm, and 65.4% of patients with PFS. The mean R2 amplitude and duration and the mean amplitude and duration of SBR were highest in patients with essential blepharospasm. The mean latency of SBR was shorter on the symptomatic side of patients with PFS when compared with the asymptomatic side. The mean R2 duration on the symptomatic side of the patients with PFS was longer than the control participants.

CONCLUSIONS

These results showed that somatosensory stimulation could be used as an alternative method to demonstrate increased excitability in facial motor neuron in patients with PFS and essential blepharospasm. Disease states relating to different peripheral and/or suprasegmental structures could also influence blink reflex and change its basal excitability and manner in which the reflex responds to modulatory factors.

Integration in working memory: a magnetic stimulation study on the role of left anterior prefrontal cortex

Integration is a fundamental working memory operation, requiring the insertion of information from one task into the execution of another concurrent task. Previous neuroimaging studies have suggested the involvement of left anterior prefrontal cortex (L-aPFC) in relation to working memory integration demands, increasing during presentation of information to be integrated (loading), throughout its maintenance during a secondary task, up to the integration step, and then decreasing afterward (unloading). Here we used short bursts of 5 Hz repetitive Transcranic Magnetic Stimulation (rTMS) to modulate L-aPFC activity and to assess its causal role in integration. During experimental blocks, rTMS was applied (N = 10) over L-aPFC or vertex (control site) at different time-points of a task involving integration of a preloaded digit into a sequence of arithmetical steps, and contrasted with a closely matched task without integration demand (segregation). When rTMS was applied during the loading phase, reaction times during secondary task were faster, without significant changes in error rates. RTMS instead worsened performance when applied during information unloading. In contrast, no effects were observed when rTMS was applied during the other phases of integration, or during the segregation condition. These results confirm the hypothesis that L-aPFC is causally and selectively involved in the integration of information in working memory. They additionally suggest that pre-integration loading and post-integration unloading of information involving this area may be active and resource-consuming processes.

A case of Bell's palsy associated with blepharospasm

BACKGROUND

Bell's palsy is the most common acute mononeuropathy, with an incidence of 20 to 30 cases per 100,000 people per year.

OBJECTIVES

Blepharospasm associated with Bell's palsy has been rarely reported. We describe an unusual presentation of Bell's palsy associated with blepharospasm.

CASE REPORT

A 44-year-old man presented to the Emergency Department with a few hours' history of right eye blepharospasm. His cornea and conjunctiva were normal on slit lamp examination, including fluorescein staining. His cranial nerves were intact except for a complete right facial nerve weakness, with the patient unable to raise his right eyebrow, and his mouth deviated towards the left. The patient was diagnosed with Bell's palsy associated with blepharospasm and discharged home on prednisone and famciclovir. By the eighth week he was back to baseline with no sequelae.

CONCLUSION

Although very rare, physicians should be aware of the existence of Bell's palsy associated with blepharospasm, as it may be under-reported.

Neurophysiology of dystonia: The role of inhibition

The pathophysiology of dystonia has been best studied in patients with focal hand dystonia. A loss of inhibitory function has been demonstrated at spinal, brainstem and cortical levels. Many cortical circuits seem to be involved. One consequence of the loss of inhibition is a failure of surround inhibition, and this appears to directly lead to overflow and unwanted muscle spasms. There are mild sensory abnormalities and deficits in sensorimotor integration; these also might be explained by a loss of inhibition. Increasing inhibition may be therapeutic. A possible hypothesis is that there is a genetic loss of inhibitory interneurons in dystonia and that this deficit is a substrate on which other factors can act to produce dystonia. This article is part of a Special Issue entitled "Advances in dystonia".