Myoclonus is a hyperkinetic, brief flexion contraction of a muscle group, resulting in a sudden jerk. Myoclonus may be epileptic or nonepileptic. Nonepileptic myoclonus is distinguished from tremor in that it is a simple contraction of an agonist muscle, whereas tremor is a simultaneous contraction of agonist and antagonist muscles. Myoclonus is seen as a manifestation of various epilepsies and of infectious, toxic, and metabolic encephalopathies. Benign myoclonus is commonly observed during sleep and may be particularly pronounced in neonates.
Tics are rapid, purposeless, involuntary, stereotyped movements and typically involve the face, eyes, shoulder, and arm. Examples of simple motor tics include blinking, nose twitching, and extremity jerking. Complex motor tics are more orchestrated movements, including head shaking, gesturing, or jumping. Phonic tics may be simple (grunting, throat clearing) or complex (uttering words, phrases). Approximately 25% of children have transient tics. Most tic disorders in children are transient and not intrusive into the child’s life, but may be a source of parental anxiety. Occasionally, tics may be unmasked by stimulant agents. Persistent motor tics (>12 months) in association with vocal tics are characteristic of Tourette syndrome, a chronic tic disorder that usually begins before age 7 years. The pathophysiology underlying tics is unknown, but a family history of tics is elicited in more than 50% of cases. Comorbid features, such as obsessive-compulsive disorder and attention-deficit/hyperactivity disorder, may be present in half of children with Tourette disorder (Chapters 13, 19). Tic disorders are clinical diagnoses, and neurodiagnostic studies have limited value. Many children with tic disorders or Tourette syndrome are unperturbed by their tics and require no therapy. Others may benefit from psychological support, including habit reversal training, and pharmacologic therapy with α-adrenergic receptor agonists (clonidine) or neuroleptics (pimozide, haloperidol, risperidone). Chronic tic disorders wax and wane regardless of intervention and most often improve substantially or resolve entirely by late adolescence.
Consciousness represents awareness of self and environment (place and time). Arousal represents the system that initiates and maintains consciousness. Consciousness is mediated by the cerebral cortex; arousal is mediated by the reticular activating system extending from the mid pons through the mid-brain and hypothalamus to the thalamus.
Lethargic patients have difficulty maintaining an arousedstate. Patients who are obtunded have decreased arousal but are responsive to stimuli. Stupor is a state of responsivenessto pain but not to other stimuli. Coma is a state of unresponsive unconsciousness and is caused by dysfunction of the cerebral hemispheres (bilaterally), the brainstem, or bothsimultaneously.
Acute Disorders of Consciousness
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Acute changes in consciousness vary in degree from mild lethargy and confusion to deep coma. In childhood, the most common causes of coma are toxins, infections, head trauma, hypoxia-ischemia (cardiac arrest, near-drowning), and seizure (postictal state, subclinical status epilepticus) (Table 184-1).
The most common cause of long-term morbidity in a patient with depressed consciousness is hypoxia; therefore, airway, breathing and circulation are addressed first. Vital signs, including pulse oximetry, must be assessed. A glucose level should also be checked immediately because hypoglycemia is a rapidly treatable cause of altered mental status. Physical examination searches for clues as to the cause of altered consciousness, such as unusual odors, needle tracts, trauma, or signs of dehydration or organ system failure.