Transient neurologic syndromes: A diagnostic approach

In somnambulism, patients exhibit complex motor behavior without interaction with their environment. Most have little recollection of the event. ⁴⁸ Sleep terrors produce a more intense reaction. The patient erupts out of sleep with profound terror, confusion, and autonomic changes. Interestingly, the patient can normally fall right back into sleep after the event. ^49–51

Back to our patient

Excessive daytime sleepiness and generalized fatigue are commonly encountered in outpatients. They can be frustrating because in many cases, no clear etiology can be discovered. ⁵²

This patient has several risk factors for parasomnias. His history of anxiety and depression in the setting of recent stressors sets the stage for night terrors. In addition, like many patients with parasomnias, he has a family history of sleep disorders. His vivid dreams make night terrors possible, but without the stark sympathetic activation it is a less likely diagnosis. It also does not account for the other symptoms he describes.

Our patient’s excessive daytime sleepiness interfering with daily activities, cataplexy, and hypnagogic hallucinations support the diagnosis of narcolepsy. This case highlights the variable weakness experienced during a cataplexy attack. It can range from a simple head droop to complete paralysis. Subtle findings require specific probing by the clinician. Patients with narcolepsy typically present in their late teens to early adulthood, but the cataplexy attacks may develop later in the disease course.

Table 3 summarizes the clinical findings associated with night terrors, somnambulism, and narcolepsy.

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.