Rhythmic palatal myoclonus (RPM) is a rare movement disorder consisting of continuous synchronous jerks of the soft palate, muscles innervated by other cranial nerves and, rarely, trunk and limb muscles. It usually develops secondary to brainstem or cerebellar disease (symptomatic RPM). Some patients, however, fail to show evidence of a structural lesion (essential RPM). A total of 287 cases with RPM from the literature including 210 cases with symptomatic and 77 cases with essential RPM have been reviewed and analysed statistically to look for criteria separating the two conditions. Patients with essential RPM usually have objective earclicks as their typical complaint which is rare in the symptomatic form. Eye and extremity muscles are never involved. The jerk frequency is lower in essential than in symptomatic RPM. Patients with essential RPM are younger and have a balanced sex distribution as compared with a male preponderance in the symptomatic form. The rhythmicity of RPM seems to be more profoundly influenced by sleep, coma and general anaesthesia in essential than in symptomatic RPM. We conclude from these results that essential RPM should be separated as a distinct clinical entity. Symptomatic RPM is a rhythmic movement disorder whose pathogenesis is quite well established. The cells of the hypertrophied inferior olives are believed to represent the oscillator. Among other possibilities, essential RPM may represent its functional analogue, based on transmitter changes only. Such a relationship could be of theoretical interest for the understanding of rhythmic hyperkinesias in general.
Facial nerve function was studied in 19 patients with hereditary motor and sensory neuropathy type I (HMSN I) and 2 patients with hereditary motor and sensory neuropathy type III (HMSN III, Dé jé rineSottas), and compared to that in 24 patients with Guillain-Barré syndrome (GBS). The facial nerve was stimulated electrically at the stylomastoid fossa, and magnetically in its proximal intracanalicular segment. Additionally, the face-associated motor cortex was stimulated magnetically. The facial nerve motor neurography was abnormal in 17 of 19 HMSN I patients and in both HMSN III patients, revealing moderate to marked conduction slowing in both the extracranial and intracranial nerve segments, along with variable reductions of compound muscle action potential (CMAP) amplitudes. The facial nerve conduction slowing paralleled that of limb nerves, but was not associated with clinical dysfunction of facial muscles, because none of the HMSN I patients had facial palsy. Conduction slowing was most severe in the HMSN III patients, but only slight facial weakness was present. In GBS, conduction slowing was less marked, but facial weakness exceeded that in HMSN patients in all cases. We conclude that involvement of the facial nerve is common in HMSN I and HMSN III. It affects the intra-and extracranial part of the facial nerve and is mostly subclinical. Hereditary motor and sensory neuropathy type I (HMSN I, Charcot-Marie-Tooth type 1) is a chronic neuropathy with onset in the first or second decade of life. 9,17,20 Muscle weakness and wasting usually begins in intrinsic foot muscles. Hand muscle involvement is usually found at a later stage, and cranial nerves are clinically spared. Hereditary motor and sensory neuropathy type III (HMSN III, Déjérine-Sottas disease) begins in childhood and is characterized by a more severe course. As in HSMN I, foot muscles are affected earlier than hand muscles, and cranial nerve involvement is rarely observed clinically. 26 Nerve conduction velocities are markedly slowed in HMSN I, and even more so in HMSN III. 13These conduction abnormalities have been characterized mainly for limb nerves, and there are only a few reports about dysfunction of cranial nerves in HMSN I. Facial nerve conduction studies concerned only the distal segment of the nerve 18 or were based on measurement of the blink reflex, 21,23,25 where the
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