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Sleep starts, also known as hypnic jerks, hypnagogic jerks, and predormital myoclonus, are benign, physiological phenomena.1-5 They usually present with motor manifestations of transient body jerks at onset of sleep, and are often triggered by fatigue, stress, and sleep deprivation.1-5Sensory manifestations have been well described as accompaniments of the movements.1 4 5 To our knowledge, the only literature reference to sensory phenomena without a body jerk is an anecdotal comment within a review article.5 We now report on two patients with purely sensory complaints restricted to onset of sleep.
Patient 1, a 42 year old college professor, had a 12 year history of 5–30 s spells occurring weekly to monthly. These episodes always occurred on falling asleep. She described mild, moderate, and severe spells as follows: mild=non-radiating electric shock-like sensation in the chest; moderate=mild plus a sense of suffocation; severe=moderate plus a poorly described medial right arm, ring, and little finger numbness. After the initial sensation, she is alerted and is then aware of the surroundings.
Patient 2, a 29 year old attorney had an eight year history of sleep onset spells lasting several minutes. These consisted of a focal itchy, sharp, pinprick-like sensation that may occur anywhere. The initial sensation awakens her and then the sensation shifts from one area to another for brief periods. There is no pattern to the location of the shifting. Scratching does not provide relief. The sensations may recur while attempting to fall asleep again. Episode frequency has increased from two to three times a year initially to once or twice a month. Changing skin care products, detergents, bedsheets, and clothing did not affect the episodes. The episodes occurred at home, as well as in other locations. Medical history was significant for migraine headaches without aura, not temporally related to the sleep onset episodes.
In both patients the spells occasionally occurred during periods of daytime sleep or drowsiness. Stress, fatigue, and sleep deprivation were often provoking factors. The sleep schedules were regular and sleep was otherwise undisturbed. Family histories were unremarkable and general physical, dermatological, and neurological examinations were normal. There was no history of recreational drug use. There was no associated tongue biting, urinary incontinence, or body movements noted at the time of initial medical evaluation. At follow up, however, patient 2 had noted a brief limb movement on two interim occasions after initial perception of the sensation. She thinks that these movements were a voluntary response to the itchiness during alerting.
The following studies were normal: patient 1, ECG, Holter monitor, brain MRI, several EEGs, a prolonged daytime sleep EEG, and polysomnography; patient 2, brain MRI.
The occurrence of sensory phenomena exclusively at onset of sleep should prompt a consideration of sensory sleep starts. The differential diagnosis includes nocturnal seizures, other parasomnias, hyperekplexia, restless legs syndrome, periodic limb movements in sleep, excessive fragmentary myoclonus, exploding head syndrome, and erroneous psychiatric diagnoses.1-5 Recognition of this unusual predormital syndrome may eliminate unnecessary diagnostic testing and avoid unnecessary anticonvulsant therapy.