Muscarine Mushroom Toxicity 

Although many mushrooms may contain cholinergic toxins like muscarine in small amounts, it is the mushrooms of the Inocybe and Clitocybe genera that contain sufficient amounts to produce a muscarinic cholinergic poisoning. In particular, Amanita muscaria is named for trace amounts of muscarine present but it does not cause clinical cholinergic toxicity.

Mushrooms that contain muscarine are commonly found in yards, parks, and wooded areas throughout the United States, Europe, and Asia. ClitocybeandInocybe genera are most commonly responsible for muscarinic mushroom poisoning in the United States. Many other species contain muscarine including Boletus, Mycena, and Omphalotus. Muscarine-containing mushrooms typically produce cholinergic symptoms such as sweating; facial flushing; salivation; lacrimation; vomiting; abdominal cramps; diarrhea; urination; miosis; and occasionally bradycardia, hypotension, and dizziness. Symptoms typically occur within 1 hour of ingestion, last for 4-24 hours, and resolve in most cases without drug therapy or with a dose of atropine.^{[1, 2]}

Muscarine was first extracted from Amanita muscaria in 1869, but this mushroom does not contain significant amounts of muscarine to cause toxicity .Ibotenic acid and muscimol are the major toxins in this mushroom and cause ethanol-like intoxication and jerking movements.

Mushroom poisoning in children is an infrequent but perennial problem for parents and clinicians. Parental anxiety is generally high because of fears of unknown or untoward effects. Clinicians are challenged to identify such poisonings, to discern whether poisoning has taken place, to order appropriate diagnostic studies, and to prescribe reasonable therapy. The varied nature of mushroom toxicities, their ubiquitous distribution, and the relative infrequency of the ingestions make the task difficult.

Several general types of mushrooms can cause poisoning:^{[3, 4, 5]}

• Cyclopeptides (eg, Amanita phalloides) - Hepatotoxic
• Orellanine and orelline (Cortinarius mushrooms) - Nephrotoxic
• Ibotenic acid and muscimol (A muscaria, A pantherina), also termed isoxazoles - Intoxication and jerking movements
• Gyromitrin or monomethylhydrazine (Gyromitramushroom) - Hemolytic
• Muscarine (Inocybe and Clitocybe mushrooms) - Cholinergic
• Coprine (Coprinus atramentarius, inky cap) - Disulfiramlike reaction
• Psilocybin (Psilocybe and Paneolus mushrooms, magic mushrooms) - Hallucinogenic
• GI irritants
• Allenic norleucine (Amanita smithiana) - Nephrotoxic
• Myotoxic (Tricholoma equestre) - Rhabdomyolysis

A classification of 14 syndromic categories of mushroom poisoning has been also proposed, but this classification system has yet to be widely adopted.^{[6, 7]}

Muscarine stimulates M1 and M2 types of postganglionic cholinergic receptors (muscarinic receptors) in the autonomic nervous system. This action results in parasympathetic stimulation similar to that caused by the release of endogenous acetylcholine at postganglionic receptors of smooth muscle and the exocrine glands, such as sweat, bronchial, lacrimal, salivary, and gastrointestinal. The action on muscarinic receptors produces a cholinergic syndrome that is characterized by sweating, bronchorrhea with shortness of breath, salivation, lacrimation, diarrhea, miosis, abdominal cramps, and bradycardia. There is negligible activity on nicotinic receptors; hence, muscle weakness, fasciculations, and paralysis are not present. Because muscarine is a quaternary amine, it does not readily cross the blood-brain barrier and does not directly cause CNS effects. Muscarine is not metabolized by cholinesterase and has a longer biologic half-life than acetylcholine.

Frequency

United States

In 2009, 5902 mushroom ingestions were reported to the National Poison Data System of the American Association of Poison Control Centers (AAPCC).^[8] Of these cases, 77% of cases involved mushrooms of unknown type. Mushrooms containing muscarine accounted for 22 cases, with 1 (5%) involving a child younger than 6 years. About 18% of all cases involving muscarine were intentional ingestions and 64% were treated at a healthcare facility. No deaths from muscarine-containing mushrooms were reported in 27 years of data collection by AAPCC.

Mortality/Morbidity

Fatalities from muscarine mushroom poisoning are very rare, and symptoms typically are mild to moderate in severity and self-limiting.

• From 1999-2009, 35 deaths due to mushrooms were reported to US poison control centers through the AAPCC, but none were attributed to muscarine mushroom poisoning.
• For the 22 exposures during 2009 to muscarine-containing mushrooms reported by US poison control centers through the AAPCC, 63% of cases had no or minor effects, 14% had moderate effects, 0% suffered severe effects, and the outcome was unknown.^[8]
• Most toxic effects of mushrooms containing muscarine are temporary and self-limiting, lasting 6-24 hours.^{[1, 2]}
• In Australia, a 53-year-old woman ate 2 large mushrooms (leftovers later identified as a Bolete mushroom, Rubinoboletus sensu lato pro tempe) and came to a hospital with a 2-hour history of headache, chest and abdominal pain, vomiting, and profuse sweating. At 3 hours, she also developed diarrhea and her condition deteriorated rapidly with hypotension, bradycardia, coma, and respiratory distress. At 7 hours, she remained in shock and did not respond to resuscitative measures. During the first hour of hemodialysis, she developed asystole and died 10 hours after ingestion. The patient's partner had eaten some of the mushrooms, but promptly vomited and did not exhibit any toxic effects.^[9] Whether this mushroom grows in North America is unknown.

Descriptions of cases reported to the North American Mycological Association, toxicology section illustrate the typical course of many mushroom poisonings; however, these cases were not necessarily observed by health care professionals.^[10]

Age

Adults are frequently involved as foragers for edible mushrooms. Because of errors in identification, they may ingest toxin-containing look-alike mushrooms. Adults and adolescents may also be inadvertently poisoned when they intentionally consume mushrooms, picked from the ground or purchased dried, to achieve intoxication. Young children may be poisoned by mushrooms when they unintentionally eat mushrooms found outside, typically in yards or outdoor play areas.