Later in life, excessive startle must be distinguished from normal sleep starts, epileptic seizures, which may begin with a startle or massive myoclonic jerk (startle epilepsy), from the multiple tic disorder, Gilles de la Tourette syndrome, of which startle may be a prominent manifestation, and from cataplexy. With idiopathic startle disease, even with a fall, there is no loss of consciousness, and the manifestations of tic and other neurologic abnormalities are absent. Reflecting the clinical proximity to myoclonus, a stimulus-evoked startle response may be a manifestation of several myoclonic neurologic diseases including Tay-Sachs disease, SSPE, “stiff-man” syndrome, lipid storage diseases and, Creutzfeldt-Jakob disease.
The mechanism of the startle response has been a matter of speculation. In animals, the origin of the phenomenon has been localized in the pontine reticular nuclei, with transmission to the lower brainstem and spinal motor neurons via the reticulospinal tracts. During the startle, the EEG may show a vertex or frontal spike–slow-wave complex, followed by a general desynchronization of the cortical rhythms; between startles the EEG is normal. Some authors have postulated a disinhibition of certain brainstem centers. Others, on the basis of testing by somatosensory evoked potentials, have suggested that hyperactive long-loop reflexes constitute the physiologic basis of startle disease (Markand et al). Wilkins and coworkers consider hyperexplexia to be an independent phenomenon (different from the normal startle reflex) and to fall within the spectrum of stimulus-sensitive myoclonic disorders. Presumably, the altered glycine receptor in startle disease is the source of some form of hyperexcitability in one or another of the motor or reticular alerting systems.
Clonazepam controls the startle disorders to varying degrees. Levetiracetam has reportedly been helpful in some patients. Also, the act of flexing the neck and bringing the arms close to the torso may reduce the intensity of an attack (Vigevano maneuver).
The focal or segmental dystonias, in contrast to the generalized dystonic disorders, are intermittent, brief or prolonged spasms or contractions of a group of adjacent muscles that places the body part in a forced and unnatural position. The most common type of focal dystonia is torticollis, a spasm that is limited to the neck muscles as detailed below. Other dystonias restricted to craniocervical muscle groups are spasms of the orbicularis oculi, causing forced closure of the eyelids (blepharospasm) and contraction of the muscles of the mouth and jaw, which may cause forceful opening or closure of the jaw and retraction or pursing of the lips (oromandibular dystonia). With the last of these conditions, the tongue may undergo forceful involuntary protrusion; the throat and neck muscles may be thrown into spasm when the patient attempts to speak or the facial muscles may contract in a grimace. Another form of dystonia that occurs independently or in association with orofacial movements is spasmodic dysphonia, a dystonia of the laryngeal muscles that imparts a high-pitched, strained quality to the voice (sometimes incorrectly termed “spastic” dysphonia) as discussed in Chap. 22. Yet a different group of focal dystonias affects the limbs, particularly the hand in relation to overuse of a small skilled movement such as writing.
To give a perspective of the relative frequencies of these disorders, of the focal dystonias seen in the movement disorder clinic of Columbia Presbyterian Hospital, 44 percent were classified as torticollis, 26 percent as spasmodic dysphonia, 14 percent as blepharospasm, 10 percent as focal dystonia of the hand (writer’s cramp), and 3 percent as oromandibular dystonia.