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668 Myasthenia Gravis and Myasthenic Syndromes

Acute General Treatment • For hypoglycemia, dextrose 5% 1-2 mL/kg/h PROGNOSIS & OUTCOME
as needed (hepatotoxic mushrooms)
Decontamination in asymptomatic animals • Blood replacement/clotting factors, • GI irritant, isoxazole, muscarinic, and
VetBooks.ir • Emesis induction (effective within a few vitamin K 1 for coagulopathy (hepatotoxic hallucinogenic mushrooms: excellent with
(p. 1087):
mushrooms)
supportive care
hours [p. 1188])
• Gastric lavage (p. 1117) can be attempted
syndrome–like signs associated with hal-
with a recent exposure to hepatotoxic or • Cyproheptadine (for dysphoria or serotonin • Hepatotoxic mushrooms: guarded to poor
with evidence of liver injury
gyromitrin mushrooms. lucinogenic mushrooms) 1.1 mg/kg PO or • Gyromitrin: guarded with hepatotoxicosis
• Activated charcoal per rectum q 6-8h prn and hemolysis
○ Use 1 g/kg with sorbitol or labeled dosage Prevent/manage liver injury (hepatotoxic • Nephrotoxic: guarded
of commercial product given PO if safe to mushrooms):
give. Repeat in 6-8 hours if hepatotoxic • N-acetylcysteine 140 mg/kg IV or PO (5% PEARLS & CONSIDERATIONS
mushrooms ingested or suspected, one-half solution), then 70 mg/kg PO q 6-8h for 7
original dose doses Comments
Manage clinical signs: • Crystalline (sodium or potassium) penicillin • Because of difficulty in differentiating toxic
• Control CNS stimulation (for hallucinogenic, G (interferes with enterohepatic recirculation from nontoxic mushrooms, any ingestion
isoxazole, hepatotoxic mushrooms) of hepatotoxins) 0.5-1 million U/kg/day for of unidentified mushrooms by pets should
○ For agitation, disorientation, acepromazine 3 days as IV CRI prompt decontamination procedures (e.g.,
0.05-0.1 mg/kg prn ○ Do not use procaine penicillin G for IV emesis, activated charcoal).
○ Diazepam 0.5-2 mg/kg IV or midazolam administration (can be fatal). • Identification of mushrooms is best done by a
0.5-1.0 mg/kg IV for seizures. Avoid • Silibinin and silymarin (extracts of milk mycologist; local college biology departments
benzodiazepine if isoxazole mushrooms thistle): veterinary formulation combines or museums are potentially useful sources
could be involved. Respiratory depres- silybin and S-adenosylmethionine (SAMe; of expertise. Internet can be used to help
sion and apnea due to potentiation of Denamarin): 20-40 mg/kg q 8-12h for 48 narrow and match pictures of the mushrooms
the muscimol-induced GABA effect may hours involved.
occur. Supportive care: • An excellent resource is the North
○ Barbiturates, other drugs if diazepam is • Thermoregulation American Mycological Association website
ineffective (p. 903) • Pain management (fentanyl, buprenorphine, (http://namyco.org/toxicology/poison
○ Pyridoxine 75-150 mg/kg slow IV for tramadol) _syndromes.html) for a case registry and a
seizures (gyromitrin mushrooms) list of local area volunteers that can help
• Atropine for excessive bronchial secretions Chronic Treatment identify the mushroom.
and bradycardia (muscarinic) 0.04 mg/kg SAMe 18 mg/kg PO q 24h for 2-3 months
(give 1 4 of dose IV, remainder IM), titrate (hepatotoxic mushrooms) Technician Tips
up as needed. Contraindicated with isoxazole Physical confinement and minimizing stimuli
mushrooms Possible Complications can be important to prevent injury for dys-
• Antiemetics Hepatic insufficiency ± hepatic encephalopathy; phoric, disoriented animals.
○ Maropitant 1 mg/kg SQ q 24h, or meto- chronic kidney disease
clopramide 0.2-0.4 mg/kg q 6h PO, SQ, SUGGESTED READING
or IM, or 1-2 mg/kg/day as constant-rate Recommended Monitoring Puschner B: Mushrooms. In Peterson ME, et al,
IV (CRI) infusion, or dolasetron 0.6-1 • Hydration, electrolytes for severe GI signs editors: Small animal toxicology, ed 3, St. Louis,
mg/kg IV q 12h • Hepatotoxic and gyromitrin mushrooms: 2013, Saunders, pp 659-676.
• Fluid diuresis for hepatotoxic/nephrotoxic CBC, liver enzymes, renal values, blood AUTHOR: Irina D. Meadows, DVM, DABT
mushrooms: fluid therapy for fluid/ glucose, coagulation parameters EDITOR: Tina Wismer, DVM, MS, DABT, DABVT
electrolyte/acid-base abnormalities for any • Nephrotoxic mushrooms: renal values
mushroom exposure as needed based on signs
(pp. 23 and 442).

Myasthenia Gravis and Myasthenic Syndromes Client Education
Sheet

BASIC INFORMATION • Acquired myasthenia gravis is fairly common • Akitas, terriers, German short-haired point-
and occurs in adult dogs; bimodal age of ers, and Chihuahuas have the highest relative
Definition onset (peaks at 3 and 10 years) risks for acquired myasthenia. German
Myasthenia gravis is skeletal muscle weakness • Acquired myasthenia gravis is uncommon shepherds and golden retrievers are also
due to a decrease of acetylcholine receptors at in adult cats. commonly affected. A familial predisposi-
neuromuscular junctions. Congenital myas- tion occurs in the Newfoundland and Great
thenic syndromes are hereditary disorders of GENETICS, BREED PREDISPOSITION Dane.
neuromuscular transmission. • Congenital myasthenic syndromes occur • Abyssinians and Somalis are at increased risk
in Jack Russell terriers, smooth fox terriers, for feline acquired myasthenia gravis.
Epidemiology golden retrievers, Labrador retrievers, and
SPECIES, AGE, SEX sporadically in other breeds. They are rare RISK FACTORS
• Congenital myasthenic syndromes are in cats. Methimazole increases the risk of acquired
uncommon; signs occur by 8 weeks of age. myasthenia gravis in cats.
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