Myasthenia gravis. Canadian Neuro- ophthalmology Group. OCULAR MYASTHENIAcontributed by Amir Ali Ahmadi and Jason Barton, University of British Columbia, January 2. EPIDEMIOLOGYMyasthenia gravis is the most common disorder of the neuromuscular junction. It has a prevalence of about 5. It has no racial or geographic predilection (1) and may occur at any age. Neonatal form are rarely encountered, and the clinical course in children and infants differ from that in adults (2). Before age 4. 0 the disease is more common in women (1). Purely ocular myasthenia, which tends to start at a slightly later age than generalized myasthenia, is more common in men (1) (3). There appears to be increased likelihood of ocular myasthenia in the. Chinese. The two classic features of myasthenic weakness are variability, in that weakness changes over minutes or days, or even shifts between different muscles, and fatigability, which means that the weakness worsens with repeated use and improves with rest. Weakness particularly affects bulbar, facial and extra- ocular muscles. One fourth of patients present with bulbar symptoms such as nasal slurred speech, or difficulty chewing and swallowing. Limb involvement is the initial complaint in a minority, about 1. The symptoms of myasthenia are often better upon awakening or after rest and will be worse after prolonged use of affected muscle later in the course of the day (6). Among the different symptoms, only two have been studied for their predictive value for myasthenia: presence of food remaining in mouth after swallowing and speech becoming unintelligible during prolonged speaking. Neither normal swallowing nor normal speech rules out myasthenia gravis (6). Fluctuating, asymmetric external ophthalmoplegia with ptosis and weak eye closure is virtually diagnostic. However, many ocular myasthenics are misdiagnosed initially. A free URL shortening and redirection service that can turn a long URL into a very short and easy to remember URL. FABI, the Forestry and Agricultural Biotechnology Institute, at the University of Pretoria, is a post-graduate research institute. Amyotrophic lateral sclerosis (ALS): three letters that change the people's life. Esclerose lateral amiotr. Attention – this is an old sales list Please check latest information exclusively on: www.fabsurplus.com Ref. Id Manufacturer Model Description Version 56026 10MW Solar Cell Line Monocyrstalline 10MW Solar Cell Mfg. Algemeen Literatuurbespreking: Aanleiding Jaarlijks wordt bij ongeveer 1.150 pati. Ondanks de vooruitgang in diagnostiek en therapie is de overleving voor pati Readbag users suggest that BOOK%20-%20DATABASE%20ON%20MEDICINAL%20PLANTS%20USED%20IN%20AYURVEDA%20-%20VOLUME%20VIII.pdf is worth reading. The file contains 560 page(s) and is free to view, download or print. Neuromuscular Junction i. Myasthenia gravis OCULAR MYASTHENIA contributed by Amir Ali Ahmadi and Jason Barton, University of British Columbia, January 2009 EPIDEMIOLOGY. Myasthenia gravis is the most common disorder of. While any ocular motility disturbance that spares the pupil and is atypical for a single nerve palsy readily suggests myasthenia, weakness patterns that fit neuropathic patterns can also be produced by myasthenia (7, 8). It is important to attend to details suggesting variability and fatigue, such as weakness worsened by activity, improved by rest, and varying daily, hourly or weekly. A diurnal pattern with worse symptoms in the evening is not uncommon. A patient who has been diagnosed with different ocular motor deficits by different physicians on different days may well have myasthenia. Although it can occur with other myopathic processes, combined weakness of the extra- ocular muscles, levator palpebrae superioris and orbicularis oculi suggests myasthenia. In one survey, 1. The International Journal of Chronic Obstructive Pulmonary Disease Ocular signs in myasthenia represent a combination of peripheral paresis and secondary central compensatory or adaptive mechanisms. Some paretic signs are highly indicative of myasthenia, particularly when they reflect excessive fatigue or variability, but compensatory signs can occur with any type of peripheral ocular weakness. An old but widely accepted classification system for myasthenia gravis is the Osserman Classification: OSSERMAN CLASSIFICATION OF MYASTHENIA GRAVISclass IOcular: purely ocular without generalized symptomsclass IIa. Mild: slow progression, drug responsive, no crisisclass IIb. Moderate: severe skeletal and bulbar involvement without crisis, less satisfactory drug responseclass IIISevere: rapid progression of severe symptoms with respiratory crisis and poor drug response. High incidence of thymoma, High Mortalityclass IVLate severe: similar to III but more time, High Mortality. Lid weakness. Fatigue and variable paretic features: In 9. It may be unilateral or bilateral, usually asymmetric initially. It is typically variable and fatigable, sometimes only apparent towards the end of the day. On exam, lid signs of fatigue include ptosis that worsens with repeated eye opening or prolonged upgaze for a minute. When the patient opens their eyes and looks straight ahead again, the rested lid will elevate well, only to droop again over the next few seconds as fatigue sets in. As with many myasthenic signs, Cogan’s lid twitch has sometimes been reported with other ocular motor disorders (1. Note the moderate left hypertropia in primary position. This pattern mimics a superior divisional III nerve palsy.(N. B. This sign of adaptation can also be found in patients with other causes of asymmetric ptosis. Occasionally, a myasthenic patient has apparent. While this can reflect co- existentthyroid orbitopathy. In response to unilateral or asymmetric ptosis, innervation to both lids increases (Hering’s law): this may cause the less affected lid to retract, which may appear more dramatic than the mild ptosis of the more affected lid (1. As with enhancement of ptosis, manual lifting of the ptotic lid will result in disappearance of the retraction, confirming that it was compensatory in origin. Likewise, the initial lid elevation in Cogan’s lid twitch can be transiently excessive (1. Last, prolonged upgaze may cause a post- tetanic facilitation leading to lid retraction in rare patients (2. Lambert- Eaton syndrome first (2. Extraocular muscles. The dynamics of eye movements show a complex mix of peripheral paretic and central adaptive effects (2. Quantitative measures have been variable, some finding mild slowing of saccades (2. Overall, the characteristics of eye movements do not adequately distinguish myasthenic weakness from other types (3. CPEO are much slower than those in myasthenia (3. Most ocular myasthenics with diplopia also have ptosis (9), but exceptions are not infrequent. Patients with extraocular weakness are usually aware of diplopia, but some complain of blurred vision. Noting that this blurriness worsens over the day and is eliminated by covering either eye will clarify the issue. Any pattern of ocular weakness can occur, from single muscle paresis to complete external ophthalmoplegia. It can mimic both peripheral palsies, such as IV palsy (7), VI palsy, and partial III palsy (8), and central ocular motor disorders, including unilateral or bilateral internuclear ophthalmoplegia (2. See Video. An upgaze palsy with intact Bell’s phenomenon can even occur, despite the fact that this usually suggests a supranuclear disorder) (2. Though any muscle may be affected, the. The peak velocity of a truncated saccade is excessive, giving the appearance of an abnormally rapid small saccade. Eye movement recordings can show moment- to- moment saccadic variability in either velocity profiles (3. Sustained gaze may cause a decrease in saccadic amplitude, but may not be specific for myasthenia (3. Fatigue and complex saccadic trajectories have also been reported in Guillain- Barre. This tonic fatigue can also cause a gaze- paretic nystagmus after prolonged gaze (4. Secondary adaptive features. Dissociated gaze- evoked nystagmus can represent compensatory changes for paresis in the other eye (4. Internal ocular muscles. There are reports of anisocoria that disappeared with anticholinesterase medication (4. These reports also claimed sluggish pupil light reactions with improvement on cholinesterase inhibitors (4. There are isolated reports of fatigue of pupil constriction to prolonged light stimulation (4. These findings are subtle and require instrumentation to detect: as a rule, obvious pupil or accommodative weakness should suggest a condition other than myasthenia. Facial Muscles. Facial weakness often coexists with ocular weakness in myasthenia, but can occur in isolation. Fatiguable weakness of the orbicularis oculi can cause. Examination may show failure to bury the lashes with forceful lid closure, or the. With profound orbicularis fatigue, the cornea may become visible. In severe cases of orbicularis weakness, there may be exposure keratitis, but this is rare. Orbicularis oris weakness may cause difficulty with whistling, sucking through straw or blowing up a balloon. On examination the patient may not be able to prevent the escape of air through the pursed lips when examiner compresses the expanded cheeks. It is assessed by having the patient push their tongue against their cheek. Slurred speech developing towards the end of a conversation is a fatigable sign. Weakness of the masseter muscles causes difficulty chewing due to poor jaw closure. Dysphagia can be due to weakness of the tongue or the posterior pharynx or soft palate; the latter can be associated with nasal dysarthria and nasal regurgitation of liquid (6). Esophageal smooth muscles are not involved. Axial Muscles. Myasthenia rarely presents with axial muscle weakness alone, but in generalized disease there can be weakness of neck flexors causing head droop, vocal cord paresis causing hoarseness, or respiratory muscle weakness causing dyspnea. The latter is a particular serious problem, as many patients who die do so from respiratory failure. Limb Muscles. Weakness affects proximal muscles mainly and is often asymmetric. There can be difficulty in raising the arms to get items off high shelves, or maintaining raised arms, as when shampooing the hair. Leg weakness can cause trouble climbing stairs, walking for long distances, or getting up out of low chairs. PATHOPHYSIOLOGYThere are congenital and acquired forms of myasthenia. Some such as familial infantile myasthenia and familal limb girdle myasthenia are autosomal recessive, others such as slow channel syndrome are autosomal dominant or sporadic. Most are apparent from birth, though the slow channel syndrome may present in adulthood. Extra- ocular muscle dysfunction is frequent but unlikely to be the sole manifestation. Sophisticated electrophysiology is required for diagnosis. Congenital myasthenia must be distinguished from neonatal myasthenia, in which the infant of a myasthenic mother has transient weakness because of placental transfer of antibodies. Acquired myasthenia is an. Antibodies directed against acetylcholine receptors of the post- synaptic membrane are responsible for the disease.
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