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Neostigmine has maximal effect in 15 to 30 minutes and it lasts for 1 to 3 hours. Edrophonium has maximal effects in 3 to 5 minutes and it lasts for 10 to 15 minutes. Neostigmine is usually preferred. These tests should be performed after choosing a quantifiable clinical sign and atropine must be readily available to eliminate the possible side-effects of neostigmine and edrophonium (bradycardia, diarrhea, and profuse tracheal secretions). Serum creatine phophokinase and cerebrospinal fluid are normal. Repetitive nerve stimulation at 10 impulses per second results in 40% decrease in motor unit potential amplitude within 1 second. These findings can be corrected by neostigmine and edrophonium. The treatment of neonatal transient myasthenia gravis consists of nasogastric feeding and respiratory support when necessary, and the use of anticholinesterase therapy. Therapy should be started with intramuscular neostigmine 0.1 mg/kg approximately 30 minutes before feeding. When the neonate is stable and swallowing well, oral neostigmine should be started at a dose of 1 mg/kg. This oral dose should be given about 1 to 2 hours prior to feeding. Neostigmine treatment is usually needed for about one month.

Hereditary Myasthenia Gravis Syndromes
Hereditary myasthenia gravis refers to a group of congenital disorders that affect the myoneural junction. They may be presynaptic or postsynaptic. Hereditary myasthenia gravis syndromes may present with sustained weakness from birth or with episodic weakness starting a few days after birth. In the latter situation, weakness usually starts several hours after waking up from sleep. Two syndromes are recognized in the neonatal period: familial infantile myasthenia gravis and congenital myasthenia gravis. Cranial nerve dysfunction is prominent in both. Signs of medullary and facial cranial nerve dysfunction predominate in familial infantile myasthenia gravis. Ocular findings predominate in congenital myasthenia gravis. Hereditary myasthenia gravis syndromes are diagnosed by observation of the response to parenteral anticholinesterase medication and a pathological decremental or incremental response to repetitive nerve stimulation.
The hereditary myasthenia gravis syndromes have autosomal recessive inheritance in most cases. They are treated with neostigmine. The dose and timing of neostigmine should be similar to that used for transient myasthenia gravis. Treatment should be continued for at least 1 year even if symptoms disappear.

 

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Fenichel, 1978 Greer, 1960 Namba, 1970 Papazian, 1997 Fenichel, 1978