teristic of the Chiari I malformation associated with a syrinx extending from C4 to D5 that did not ... Institute of Neuroscience,. Psychiatric and Anesthesiological ...
© Springer-Verlag 2001
Neurol Sci (2001) 22:27-29 C A S E R E P O RT
S. Bagnato • V. Rizzo • A. Quartarone • G. Majorana • G. Vita • P. Girlanda
Segmental myoclonus in a patient affected by syringomyelia
Received: 23 January 2001 / Accepted in revised form: 24 April 2001
Abstract We describe a patient who has been complaining of brief jerk-like, rhythmic, involuntary movements involving the second digit of the left hand for the last three months. These involuntary jerks produced an adduction movement of the second digit and were unaffected by peripheral sensory stimuli. In addition, the patient experienced loss of dexterity in the left hand. On examination the patient showed hypotrophy of the first dorsal interosseous (FDI) muscle of the left hand and a dissociated sensory loss involving the C8-T1 dermatomes. Magnetic resonance imaging of the brain and spinal cord revealed a tonsilar herniation characteristic of the Chiari I malformation associated with a syrinx extending from C4 to D5 that did not communicate with the fourth ventricle. The electrophysiological evaluation indicated the presence of a focal myoclonus of spinal origin that is likely to be caused by the syrinx.
Introduction
Key words Segmental myoclonus Neurophysiological investigation
Case report
S. Bagnato () • V. Rizzo • A. Quartarone G. Majorana • G. Vita • P. Girlanda Institute of Neuroscience, Psychiatric and Anesthesiological Sciences Policlinico Universitario I-98125 Messina, Italy
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Syringomyelia
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Segmental myoclonus is characterized by rhythmic or arrhythmic involuntary contractions of muscle groups, usually agonists, supplied by one or several contiguous segments of the brain stem (branchial myoclonus) or spinal cord (spinal myoclonus) [1]. Segmental myoclonus has been considered relatively unaffected by supraspinal influences but some authors have reported an increase in amplitude or frequency of the jerks with action or mental stress [2]. Spinal myoclonus may have different causes such as spinal tumors, vascular myelopathies, viral infections, or trauma to the spinal cord [3]. As far as we know, there are only a few reports about spinal myoclonus as related to syringomyelia [4, 5].
We describe a 48-year-old man who has been complaining of brief jerk-like, rhythmic, involuntary movements involving the second digit of the left hand for the last three months. These involuntary jerks produced an adduction movement of the second digit and were unaffected by sensitive stimuli. The jerks disappeared during sleep and worsened after mental stress or fatigue. In addition, the patient experienced loss of skillfulness in the left hand and suboccipital pain which worsened with coughing or sneezing. Neurological examination revealed hypotrophy of the left first dorsal interosseus (FDI) muscle and a dissociated sensory loss involving pain and temperature alone in the C8-T1 dermatomes on the left side. Magnetic resonance imaging (MRI) of the brain and spinal cord revealed a tonsillar herniation characteristic of the Chiari I malformation associated with a syrinx extending from C4 to D5 that did not communicate with the forth ventricle. The patient underwent an electrophysiological protocol consisting of concentric needle electromyography (EMG), somatosensory evoked
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S. Bagnato et al.: Segmental myoclonus in a patient affected by syringomyelia
potential (SEP), polygraphic recordings, backaveraging of the involuntary movements, peripheral silent period and recovery cycle of the R2 of the blink reflex. Concentric needle electromyography revealed chronic partial denervation in the C8- and T1-supplied muscles of the left hand. The somatosensory evoked potentials performed after stimulation of the left median nerve revealed normal P14 and N20 while the N13, obtained after glottis reference, was nearly abolished. Concentric needle EMG recordings, simultaneously performed on the left first dorsal interosseous and left abductor pollicis brevis muscles, showed synchronous bursts of potentials in both muscles lasting about 500 ms. The firing rate of these bursts was 1.5/s (Fig. 1). Backaveraging technique
demonstrated that the jerks were not preceded by electroencephalographic activity in the contralateral sensory motor cortex. The recovery cycle of the blink reflex, after paired shocks applied on the supraorbital nerve, was normal. The peripheral silent period, obtained after supramaximal stimulation of the ulnar and median nerves at the wrist (250 V, 0.2 ms duration), was absent on the left side (Fig. 2a) and of normal duration in the opposite arm (Fig. 2b). Transcranial magnetic stimulation, using a 9-cm round coil, did not produce any variation on the jerk’s occurence. The patient underwent surgical operation with a partial reduction of involuntary movements and improvement of the dexterity. The patient refused symptomatic treatment with clonazepam.
Fig. 1 Electromyogram demonstrating 1.5 Hz rhythmic contractions in first dorsal interosseus (FDI) and abductor polli (ABP) muscles lasting about 500 ms
Fig. 2 Peripheral silent period after supramaximal electrical stimulation of ulnar nerve at the wrist and recording from FDI muscle. The top three traces refer to the affected side. Note the presence of the silent period on the spared side (lower three traces)
S. Bagnato et al.: Segmental myoclonus in a patient affected by syringomyelia
Discussion The main finding of our study is that a central spinal cord lesion such as a syrinx may predispose to spinal motor neuron hyperexcitability. The patient had typical rhythmic segmental myoclonus. There was no evidence of cortical or brainstem hyperexcitability because the cortical SEP waveforms were normal in amplitude and the recovery cycle of blink reflex was unaltered. Moreover, the backaveraging of involuntary movements did not reveal any EEG activity in the contralateral sensorimotor cortex. These results, along with the segmental distribution, suggest a spinal origin of the myoclonus. The pathophysiology of spinal myoclonus remains speculative. The clinical characteristics of spinal myoclonus suggest that it is the result of repetitive, spontaneous discharges of groups of anterior horn cells [6]. It may be postulated that the syrinx produces a hyperexcitability of alpha motoneurons due to direct cellular damage or to removal of inhibition [7]. In patients with myoclonus after ischemic damage of the spinal cord, histological studies have shown a massive reduction in the number of small- and medium-sized neurons in the posterior horns [8]. The majority of these interneurons are inhibitory, and the loss of these cells may increase the excitability of alpha motoneurons. Further evidence suggesting a loss of spinal interneurons has been provided by Di Lazzaro et al. [9] who, in patients affected by spinal myoclonus, reported that the recovery cycle of the N22 component, after stimulation of the peroneal nerve, is impaired with less inhibition. In our patient the peripheral silent period, obtained after stimulation of the ulnar and median nerves on the left side, was absent while it was normally induced on the opposite side. The silent period following electrical stimulation of a peripheral nerve in a contracting muscle is the result of a sequence of events implying spinal inhibitory mechanisms such as after hyperpolarization, activation of recurrent inhibition, Golgi tendon organ activation and excitation of cutaneous fibers [10]. In conclusion, our data suggest that a syrinx may induce the hyperexcitability of alpha motoneurons probably due to loss of inhibitory spinal interneurons and therefore cause the occurrence of the spinal myoclonus.
Sommario Viene descritto il caso di un paziente di 48 anni che presentava movimenti ritmici ed involontari a carico del
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secondo dito della mano sinistra. Tali movimenti determinavano l’adduzione di tale dito e non si modificavano in risposta a stimoli sensitivi. Il paziente riferiva inoltre impaccio motorio a carico della mano sinistra. L’esame neurologico dimostrava la presenza di ipotrofia a carico del muscolo primo interosseo dorsale della mano sinistra e di ipoestesia termo-dolorifica nei dermatomeri C8-D1 con integrità della sensibilità tattile. Uno studio RM dell’encefalo e del midollo spinale rivelava l’esistenza di un’erniazione delle tonsille cerebellari, caratteristica della malformazione di Chiari tipo I, con associata una cavità siringomielica estesa da C4 a D5 non comunicante con il quarto ventricolo. Lo studio elettrofisiologico praticato è risultato indicativo di un mioclono focale di origine spinale causato, verosimilmente, dalla cavità siringomielica.
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