Belly dance syndrome due to spinal myoclonus.

We report on a case of spinal myoclonus resembling a belly dance syndrome.     

Neurologic disorders affecting the anorectum

Neurologic disorders that affect the brain, spinal cord, or extrinsic innervation may present with similar symptoms and share common pathophysiology, such as rectal impaction, loss of an urge to defecate, inability to trigger a defecation sequence, obstructive defecation, or incontinence. If these symptoms are persistent or bothersome, they require treatment. The management of a patient with neurologic anorectal dysfunction depends on the underlying pathophysiologic mechanisms. Dietary advice, bowel training, pharmacotherapy, and rehabilitative treatment may be used alone or in combination.     

Multiple firing of motoneurones is produced by cortical stimulation but not by direct activation of descending motor tracts.

In the present report we have tested whether stimulation of the motor descending tracts at the brain-stem level could set up repetitive motor unit discharges in a similar manner to that described for motor cortical stimulation. We have seen that a large descending motor volley, evoked by brain-stem stimulation, cannot produce repetitive firing of motor units. Repetitive motoneurone firing is therefore produced by multiple excitatory volleys set up by single cortical shocks.     

Ovarian hormones and cortical excitability. An rTMS study in humans.

OBJECTIVE: Ovarian steroids influence neural excitability. Using repetitive transcranial magnetic stimulation (rTMS) we investigated changes in cortical excitability during the menstrual cycle. METHODS: Eight women underwent rTMS on Days 1 and 14 of the menstrual cycle. As a control group, 8 age-matched men were also tested twice, with a 14-day interval between the two experimental sessions. Repetitive magnetic pulses were delivered in trains of 10 stimuli (5 Hz frequency and 120% of the motor threshold calculated at rest) to the left motor area of the first dorsal interosseous muscle. RESULTS: In women, the motor evoked potential (MEP) size did not increase on Day 1, but it increased progressively during the train on Day 14. The duration of the silent period progressively lengthened during the train on both days. In men the MEP increased in size, and the silent period lengthened to a similar extent on both days. CONCLUSIONS: In women, hormone changes related to the menstrual cycle alter cortical excitability. SIGNIFICANCE: Low estrogen levels probably reduce cortical excitability because their diminished action on sodium channels reduces recruitment of excitatory interneurons during rTMS thus abolishing the MEP facilitation.     

Pathophysiology of hemimasticatory spasm.

Two patients aged 21 and 50 years presented with facial hemiatrophy and unilateral spasms of the masticatory muscles. Masticatory muscle biopsy showed normal findings in both patients and facial skin biopsy specimens only showed atrophy, although morphoea (localised facial scleroderma) had been diagnosed nine years previously in the second patient. The involuntary movements consisted of brief twitches and prolonged contractions clinically and electromyographically similar to those of hemifacial spasm and cramps. The jaw jerk and the silent periods were absent in the affected muscles. Direct stimulation of the muscle nerve and transcranial stimulation of the trigeminal root demonstrated slowing of conduction and after-activity due to autoexcitation. Observations in other reported cases and these two patients suggest that hemimasticatory spasm is produced by ectopic activity secondary to focal demyelination of the trigeminal motor nerve fibres. The proposed cause of the neuropathy is focal damage to the masticatory nerves caused by compression, possibly resulting from the deep tissue changes that occur in facial hemiatrophy.     

The limits of tooth pulp evoked potentials for pain quantitation

Tooth pulp evoked potentials (TPEPs0 and subjective evaluation of painful dental stimuli have been recorded in healthy volunteers. The amplitude of TPEPs late components and the subjective rating have been studied in different psychological states, by changing the expectancy of pain with a placebo and by providing foreknowledge of stimulus timing with self-stimulation. The placebo induced a significant depression of TPEPs and pain sensation. The amplitude of TPEPs evoked by self-delivered stimuli was reduced but the subjective report remained unchanged. These results demonstrate that TPEPs are not a stable correlate of the pain perceived or of the painful input.     

Ia presynaptic inhibition after muscle twitch in the arm

Contraction of upper limb muscles in healthy subjects was used to investigate presynaptic inhibition at spinal level. The H reflex recorded in the forearm flexor muscles in response to median nerve stimulation was depressed in amplitude from 400 ms to 1 s after a muscle twitch induced by transcranial stimulation, root stimulation, direct biceps stimulation, and triceps tendon tap. Stimulation of the cutaneous branch of musculocutaneous nerve, ipsilateral triceps and contralateral biceps, and biceps tendon tap did not alter H-reflex size. Forearm flexor H-reflex amplitude is therefore related to changes in proprioceptive inflow secondary to the biceps muscle twitch. Root and direct muscle stimulation both failed to reduce the size of the motor evoked potential (MEP) after transcranial magnetic stimulation, suggesting that the inhibition acts at presynaptic level. Attenuation of H-reflex amplitude was related to the size of the muscle twitch and was less pronounced during an isometric twitch than during free joint movement. Our results suggest that the biceps muscle twitch produces long-lasting inhibition of the Ia afferents from forearm flexor muscles. This is an important and a simple mechanism for suppressing proprioceptive input during movement.     

Attention influences the excitability of cortical motor areas in healthy humans

We investigated whether human attentional processes influence the size of the motor evoked potentials (MEP) facilitation and the duration of the cortical silent period (CSP) elicited by high-frequency repetitive transcranial magnetic stimulation (rTMS). In healthy subjects we assessed the effects of 5 Hz-rTMS, delivered in trains of 10 stimuli at suprathreshold intensity over the hand motor area, on the MEP size and CSP duration in different attention-demanding conditions: “relaxed,” “target hand,” and “non-target hand” condition. We also investigated the inhibitory effects of 1 Hz-rTMS conditioning to the premotor cortex on the 5 Hz-rTMS induced MEP facilitation. F-waves evoked by ulnar nerve stimulation were also recorded. rTMS trains elicited a larger MEP size facilitation when the subjects looked at the target hand whereas the increase in CSP duration during rTMS remained unchanged during the three attention-demanding conditions. The conditioning inhibitory stimulation delivered to the premotor cortex decreased the MEP facilitation during the “target hand” condition, leaving the MEP facilitation during the other conditions unchanged. None of the attentional conditions elicited changes in the F wave. In healthy subjects attentional processes influence the size of the MEP facilitation elicited by high-frequency rTMS and do so through premotor-to-motor connections.