פרק 46 Chapter 46: Disorders of the Neuromuscular Junction, Myotonias, and Persistent Muscle Fiber Activity Flashcards

Question

Answer 1

החולה תזדקק לעלייה במינון פירידוסטיגמין The weakness and atrophy of chronic thyrotoxic myopathy may be added to that of the myasthenia without appearing to affect the requirement for or response to anticholinesterase medications. By contrast, **hypothyroidism**, even of mild degree, seems to **aggravate the weakness of myasthenia gravis, greatly increasing the need for pyridostigrnine and at times inducing a myasthenic crisis.**

Answer 2

פלזמה פרזיס- מדובר בהחמרה אקוטית של מיאסטניה לאחר מחלה ריאתית.

Answer 3

נוגדני אנטי מאסק

Answer 4

פניצילאמין There are more than 30 drugs in current clinical use (other than anesthetic agents) that may, under certain circumstances, interfere with neuromuscular transmission in otherwise normal individuals. Of these, the most important are the **aminoglycoside and quinolone** antibiotics. Myasthenic weakness has been reported with 18 different antibiotics but particularly **neomycin, kanamycin (less so with gentamicin), colistin, streptomycin, polymyxin B, and certain tetracyclines**. It has been shown that these drugs **impair transmitter release by interfering with calcium ion fluxes** at nerve terminals (**Presynaptic**). The **fluoroquinolones**—typified by **ciprofloxacin**—affect both **pre and postsynaptic activity** Other agents—particularly the **organophosphate insecticides and nerve gases**—cause paralysis by binding to **cholinesterase and blocking the hydrolysis of Ach**. The endplate remains **depolarized and is refractory** to neural stimuli. The most notable of these agents are (1) **botulinum** toxin, which binds to cholinergic motor endings, **blocking quantal release of Ach**; (2) **black widow spider venom**, which causes a **massive release of Ach**, resulting in muscular contraction and then **paralysis from a lack of Ach**; (3) **d-tubocurarine**, which **binds to AChR**; (4) **suxamethonium and decamethonium**, which also bind to **AChR**; (5) **organophosphates**, which bind ***irreversibly to AChE***; (6) **malathion and parathion**, which **inhibit AChE**. The actions of all these agents except for the organophosphate “nerve gases” are transitory. * The administration of **d-penicillamine** has also caused an unusual type of myasthenia- **induced autoimmune myasthenia gravis** seropositive. Rarely, typical autoimmune myasthenia gravis develops as part of a chronic graft-versus-host disease in long-term (2- to 3-year) survivors of allogeneic marrow transplants. A large group of naturally occurring environmental neurotoxins are known to act at the neuromuscular junction and to induce muscle paralysis of a pattern like that of myasthenia gravis. Venoms of certain snakes, spiders, and ticks are common and well-known animal poisons, as are ciguatera and related toxins (from fish that have ingested certain dinoflagellates), curare (from plants), and Clostridium botulinum

Answer 5

בעת הרמת עפעף צנוח תהיה צניחה של העפעף הקונטראלטרלי **Particular ocular signs** are highly characteristic of myasthenia. For example, **sustained upgaze** (for 30 or more seconds) will usually **induce or exaggerate ptosis and may uncover myasthenic ocular motor weakness**, thereby marking it as “fatigable.” **twitching of the upper eyelid** that appears a moment after the patient moves the eyes from a **downward to the primary position (“*lid-twitch” sign***). *one or more twitches may be observed upon closure of the eyelids or during horizontal movements of the eyes*. Repeated ocular versions when tracking a target or by an optokinetic stimulus may disclose progressive paresis of the muscles that carry out these movements. Unilateral painless ptosis without either ophthalmoplegia or pupillary abnormality in an adult will most often prove to be due to myasthenia. Usually, there is **subtle ptosis of the other eye that can be revealed by manually elevating the more affected eyelid**. Attempts by the patient to overcome ptosis may impart a staring expression of the opposite eye. Bright sunlight is said to aggravate the ocular signs and cold to improve them. The application of an ice pack over the eye often relieves the ptosis for a brief period.

Answer 6

הפרעה בתפקוד חיבור עצב שריר **Particular ocular signs** are highly characteristic of myasthenia. For example, **sustained upgaze** (for 30 or more seconds) will usually **induce or exaggerate ptosis and may uncover myasthenic ocular motor weakness**, thereby marking it as “fatigable.” **twitching of the upper eyelid** that appears a moment after the patient moves the eyes from a **downward to the primary position (“*lid-twitch” sign***). *one or more twitches may be observed upon closure of the eyelids or during horizontal movements of the eyes*. Repeated ocular versions when tracking a target or by an optokinetic stimulus may disclose progressive paresis of the muscles that carry out these movements. Unilateral painless ptosis without either ophthalmoplegia or pupillary abnormality in an adult will most often prove to be due to myasthenia. Usually, there is **subtle ptosis of the other eye that can be revealed by manually elevating the more affected eyelid**. Attempts by the patient to overcome ptosis may impart a staring expression of the opposite eye. Bright sunlight is said to aggravate the ocular signs and cold to improve them. The application of an ice pack over the eye often relieves the ptosis for a brief period.

Answer 7

neonatal myasthenia gravis אינה מועברת בתורשה דומיננטית. An **estimated 10 to 20 percent of babies born to mothers with myasthenia show transient signs of myasthenia** (hypotonia, weak cry and suck). This transitory phenomenon is apparent at birth and has a **mean duration of about 2 to 5 weeks**; recovery is usually **complete within 2 months of birth** (rarely longer), without later relapse. Uncommonly, the mother with myasthenia reports reduced intrauterine movements, suggesting a dangerous degree of myasthenia in the fetus. A few of these children will be born with **arthrogryposis**, the result of a sustained period of intrauterine immobility, and this complication tends to recur in subsequent births. It has long been assumed that neonatal myasthenia is a result of the **passive transplacental transfer of AChR antibodies**. This explanation is not entirely satisfactory insofar as maternal AChR antibodies are transferred from mother to fetus in all AChR antibody-positive pregnancies and the *incidence and severity of neonatal myasthenia gravis do not correlate with the severity or duration of the mother's illness or with the serum level of the maternal AChR antibody*. In fact, neonatal myasthenia may occur when the mother is in remission. **Administration of plasma exchange and anticholinesterase drugs to the infant may be useful in hastening recovery from neonatal myasthenia.**

Answer 8

העברת נוגדנים An **estimated 10 to 20 percent of babies born to mothers with myasthenia show transient signs of myasthenia** (hypotonia, weak cry and suck). This transitory phenomenon is apparent at birth and has a **mean duration of about 2 to 5 weeks**; recovery is usually **complete within 2 months of birth** (rarely longer), without later relapse. Uncommonly, the mother with myasthenia reports reduced intrauterine movements, suggesting a dangerous degree of myasthenia in the fetus. A few of these children will be born with **arthrogryposis**, the result of a sustained period of intrauterine immobility, and this complication tends to recur in subsequent births. It has long been assumed that neonatal myasthenia is a result of the **passive transplacental transfer of AChR antibodies**. This explanation is not entirely satisfactory insofar as maternal AChR antibodies are transferred from mother to fetus in all AChR antibody-positive pregnancies and the *incidence and severity of neonatal myasthenia gravis do not correlate with the severity or duration of the mother's illness or with the serum level of the maternal AChR antibody*. In fact, neonatal myasthenia may occur when the mother is in remission. **Administration of plasma exchange and anticholinesterase drugs to the infant may be useful in hastening recovery from neonatal myasthenia.**

Answer 9

הטיפול הוא אטרופין סולפאט- מדובר ב cholinergic crises . If the response to anticholinesterase drugs is poor and progressively larger doses are not relieving symptoms, there is consideration of a **cholinergic crisis**. In our own experience with more than 80 patients of severe myasthenia in an intensive care unit, we have been persuaded of the occurrence of a cholinergic crisis only rarely. This consists of a **relatively rapid increase in muscular weakness, usually coupled with the adverse muscarinic *effects of the anticholinesterase drug*** (**nausea, vomiting, pallor, sweating, salivation, bronchorrhea, colic, diarrhea, miosis, bradycardia**). An impending cholinergic effect is betrayed by **constriction of pupils**. If the **blood pressure falls with bradycardia, 0.6 mg atropine sulfate may be given slowly by the intravenous route**. Neostigmine or repetitive stimulation may be used to determine whether or not weakness is to the result of an excess of anticholinesterase medications.

Answer 10

הפרעה פרה-סינפטית בכמות הוזיקולות של אצטיל כולין

פרק 46 Chapter 46: Disorders of the Neuromuscular Junction, Myotonias, and Persistent Muscle Fiber Activity Flashcards

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