MRI assessment of children with obsessive-compulsive disorder or tics associated with streptococcal infection.

OBJECTIVE: The authors assessed selective basal ganglia involvement in a subgroup of children with obsessive-compulsive disorder (OCD) and/or tics believed to be associated with streptococcal infection. METHOD: Using computer-assisted morphometric techniques, they analyzed the cerebral magnetic resonance images of 34 children with presumed streptococcus-associated OCD and/or tics and 82 healthy comparison children who were matched for age and sex. RESULTS: The average sizes of the caudate, putamen, and globus pallidus, but not of the thalamus or total cerebrum, were significantly greater in the group of children with streptococcus-associated OCD and/or tics than in the healthy children. The differences were similar to those found previously for subjects with Sydenham's chorea compared with normal subjects. CONCLUSIONS: These results support the hypothesis that there is a distinct subgroup of subjects with OCD and/or tics who have enlarged basal ganglia. These findings are consistent with the hypothesis of an autoimmune response to streptococcal infection.

Post-stimulation effects of high-frequency stimulation on sensory discharge from muscle.

Previously the application of stimuli of 600 Hz at adjustable strength applied to a muscle's nerve has been proposed as a means of reducing the muscle's contraction in spastic conditions, or when combined with a second tetanic stimulation, of limiting contraction to smaller, physiologically more relevant motor units in the paralyzed state. The side-effects on muscle spindles of such stimuli as seen in the cat's gastrocnemius are reported. During stimulation axonal impulses followed faithfully for periods running into minutes. After stimulation, a pause in ongoing firing with a duration dependent on stimulus-train length and a two-phased recovery occurred. Responses to dynamic stretch of the muscle were affected as well. The contractions of intrafusal fibers activated in several ways was seen to strongly offset the depression. In a clinical application, nevertheless, short-lived depression of all proprioceptive modalities following stimulation should be expected, with corresponding disturbance on sensory perception and reflex effects.