Transient neurologic syndromes: A diagnostic approach
ABSTRACT
Clinicians are often confronted with patients who have transient neurologic symptoms lasting seconds to hours. In many of these patients, their symptoms have gone away or returned to baseline by the time of evaluation, making the diagnosis even more challenging. Elements such as correlation of symptoms with vascular territory, prodromes, triggers, motor symptoms, confusion, and sleep behavior can guide the diagnostic workup.
KEY POINTS
- Transient ischemic attack, migraine aura, and partial seizures are common and often can be differentiated by their distinctive symptoms.
- Episodes of confusion in a patient with diabetes raise the possibility of hypoglycemic encephalopathy; other possibilities include hyperventilation syndrome and transient global amnesia.
- Daytime sleepiness in a young patient may be due to narcolepsy or parasomnias.
RARE CAUSES OF TRANSIENT NEUROLOGIC SYMPTOMS
Transient (paroxysmal) neurologic events in multiple sclerosis
A less well-known phenomenon in multiple sclerosis is termed “transient” (paroxysmal) neurologic events. These are typically stereotyped episodes lasting seconds, occurring sometimes hundreds of times a day. They are thought to arise from spontaneous electrical activity in an area of demyelination (ephaptic transmission), creating a wide range of symptoms. Some common events include positive sensory symptoms, alteration of the motor system such as spasms, or brainstem symptoms.53
Channelopathy
Two prototypical channelopathies are hyperkalemic and hypokalemic periodic paralysis. They are rare conditions, usually inherited in an autosomal dominant pattern.54 Both produce episodic, flaccid weakness in the setting of activity or other stressors (fasting, pregnancy, an emotionally charged episode). The attacks last a few minutes to hours and affect proximal skeletal muscles, with very little respiratory or bulbar involvement.
Hyperkalemic periodic paralysis is also associated with myotonia, which is the inability to voluntarily relax after stimulation. This can be evident after shaking a patient’s hand, as he or she would be unable to release because of the sustained activation. The myotonia is evident between attacks and may help cue a physician to the diagnosis even if the weakness has abated.55
As the name implies, potassium levels can vary during the attack, though hyperkalemic periodic paralysis can be seen with normal levels of serum potassium. The underlying pathology is tied to a voltage-gated sodium channel or calcium channel necessary for action potential generation.56
Paroxysmal dyskinesias
Paroxysmal dyskinesias encompass a rare group of movement disorders characterized by attacks without alterations in consciousness. Patients have reported dystonic, choreoathetotic, or ballistic movements. The attacks can be triggered by stress, eating, or even other types of movements. Most reported cases have a strong family history and are inherited in an autosomal dominant pattern. The exact pathophysiology is unclear. When paroxysmal dyskinesia was initially discovered, many thought it was a form of epilepsy, but the lack of electroencephalographic changes and postictal events argues against this etiology.
Transient focal neurologic episodes in cerebral amyloid angiopathy
Cerebral amyloid angiopathy is a degenerative condition in which amyloid is deposited in cerebral vessels, making them friable and at risk of bleeding. Most patients have no symptoms whatsoever, and the diagnosis is made by magnetic resonance imaging. Small microbleeds are common, but lobar intraparenchymal hemorrhage is the most feared complication.
Transient focal neurologic episodes, sometimes termed “amyloid spells,” are recurrent, stereotyped neurologic events that are spurred by cortical superficial siderosis (deposition of iron). Unfortunately, these events are difficult to characterize by their clinical morphology. The events can involve the visual, motor, and sensory pathways with both positive and negative symptoms, making the diagnosis difficult without imaging. These events may precede a symptomatic intraparenchymal hemorrhage, offering a unique window to reconsider the decision to continue an antiplatelet or anticoagulant drug.57,58
