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  • Updated 09.10.2021
  • Expires For CME 09.10.2024

Neurologic presentations of mushroom poisoning: overview

Introduction

Overview

Only a small fraction of known species of fungi is hazardous. Nevertheless, even if some species are considered edible, low concentrations of toxins can still be present, and either chronic ingestion or overconsumption can result in manifest toxicity. Thus, mushrooms and other higher fungi can be divided into edible, conditionally edible, and poisonous categories. For the conditionally edible group, edibility depends either on controlling both the frequency and amount of fungi ingested or on the elimination (where possible) of toxins by drying, soaking, cooking, and other pretreatments. At least 8 distinct neurologic or myologic presentations of mushroom poisoning have been reported: (1) acute encephalopathy; (2) hallucinations; (3) CNS dysfunction, including cerebellar dysfunction; (4) seizures; (5) cholinergic (muscarinic) syndrome; (6) erythromelalgia; (7) a disulfiram-like reaction; and (8) rhabdomyolysis. Some mushroom toxins produce their associated toxidromes by affecting neurotransmission. Except for the myotoxic and false morel neurologic toxidromes, neurologic and myologic presentations of mushroom poisoning are rarely fatal. Fatalities have uncommonly occurred with other neurologic toxidromes (eg, cholinergic mushroom poisoning). Other serious and often permanent organ dysfunction or fatalities may result from accidentally ingesting a more toxic mushroom resembling one that is hallucinogenic, edible, or conditionally edible.

Key points

Only a small fraction of known species of mushrooms is hazardous.

Even if some species are considered edible, low concentrations of toxins can still be present, and either chronic ingestion or overconsumption can result in manifest toxicity.


Mushrooms and other higher fungi can be divided into edible, conditionally edible, and poisonous categories.


At least 8 distinct neurologic or myologic presentations of mushroom poisoning have been reported: (1) acute encephalopathy; (2) hallucinations; (3) CNS dysfunction, including cerebellar dysfunction; (4) seizures; (5) cholinergic (muscarinic) syndrome; (6) erythromelalgia; (7) a disulfiram-like reaction; and (8) rhabdomyolysis.


Although for most neurologic and myologic presentations of mushroom poisoning, care is primarily supportive and symptomatic, specific management is needed for some.


Some mushroom toxins produce their associated toxidromes by affecting neurotransmission.


Except for the myotoxic and false morel neurologic toxidromes, neurologic and myologic presentations of mushroom poisoning are rarely fatal.


Other serious and often permanent organ dysfunction or fatalities may result from accidentally ingesting a more toxic mushroom resembling one that is hallucinogenic, edible, or conditionally edible.

Historical note and terminology

Scope. For this article, we consider neurotoxins and myotoxins originating in macroscopic higher fungi that are either intentionally or accidentally ingested. Some, but not all, of the responsible toxic fungi are stalked mushrooms (or toadstools); mushrooms are a subset of fungi from the phylum Basidiomycota (which also includes other fungi with nonmushroom structures like puffballs, bracket fungi, etc.), whereas the Ascomycota include a range of nonmushroom structures. Somewhat colloquially, we will consider the effects of ingesting these mushroom toxins collectively as mushroom poisoning.

So-called mycotoxins (eg, ergotamine) are not covered in this chapter. Like mushroom toxins (or poisons), mycotoxins are a chemically and pharmacologically heterogeneous assemblage of low-molecular-weight natural products produced as secondary metabolites by filamentous fungi. The definition of a mycotoxin, however, does not correctly apply to all fungal substances that are toxic to humans, other animals, or plants, even if some physicians (mis)use the terminology to refer to all fungal toxic substances as mycotoxins, including those produced by mushrooms (03; 04):


Other low-molecular-weight fungal metabolites such as ethanol that are toxic only in high concentrations are not considered mycotoxins. ... [In addition], although mushroom poisons are definitely fungal metabolites that can cause disease and death in humans and other animals, they are rather arbitrarily excluded from discussions of mycotoxicology. ... The distinction between a mycotoxin and a mushroom poison is based not only on the size of the producing fungus, but also on human intention. Mycotoxin exposure is almost always accidental. In contrast, with the exception of the victims of a few mycologically accomplished murderers [and accidental mushroom poisoning cases in young children], mushroom poisons are usually ingested by amateur mushroom hunters who have collected, cooked, and eaten what was misidentified as a delectable species (02). [emphasis added]

Classification of fungi. Within the kingdom Fungi is the subkingdom Dikarya (often referred to as the higher fungi). Dikarya includes two large divisions or phyla: Basidiomycota and Ascomycota.

Basidiomycota. Basidiomycota are filamentous fungi composed of hyphae and reproduce sexually. Basidiomycota includes inter alia some fungi that might be grown or foraged for food (eg, mushrooms, puffballs, bracket fungi, other polypores, and chanterelles) and fungi that infest plants and might be secondarily ingested (eg, smuts, bunts, rusts).

Ascomycota. Ascomycota, commonly known as the sac fungi, are defined by an ascus (meaning sac or wineskin), a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual. Familiar edible or conditionally edible examples of sac fungi include morels and truffles, whereas others with much greater potential toxicity include false morels and Claviceps purpura (ergot).

Only a small fraction of known species of mushrooms is hazardous. Nevertheless, even if some species are considered edible, low concentrations of toxins can still be present, and either chronic ingestion or overconsumption can result in manifest toxicity. Thus, mushrooms and other higher fungi can be divided into edible, conditionally edible, and poisonous categories (12). For the conditionally edible group, edibility depends either on controlling both the frequency and amount of fungi ingested or on the elimination (where possible) of toxins by drying, soaking, cooking, and other pretreatments.

Classification of mushroom poisoning. Multiple classification systems for mushroom poisoning have been proposed (Table 1) (01; 06; 21; 13). Almost all of these consider fungal toxidromes for both mushroom and nonmushroom forms of higher fungi. However, most of these classifications do not address neurotoxic presentations very thoroughly or effectively, nor have they kept up with subsequent descriptions of various novel toxidromes or the elaboration (in some cases) of the responsible toxins.

Table 1. Neurologic Components Of Different Classifications Of Mushroom Poisoning

Barbato, 1993 (01)


Group B muscarine (cholinergic toxidrome)


Group C Psilocybin (hallucinogenic toxidrome)


Group D Muscimol (confusion, ataxia, and hallucinations)


Group F Coprine (disulfiram-like reaction)

Blackman, 1994 (06)


Group 2 Gyromitrin (monomethylhydrazine) poisoning


Group 3 Coprine poisoning


Group 4 Muscarine poisoning


Group 5 Ibotenic acid -- Muscimol poisoning


Group 6 Psilocybin poisoning (magic mushrooms)

White, 2019 (21)


Group 2 - Neurotoxic mushroom poisoning
Group 2A - Hallucinogenic mushrooms (psilocybin)
Group 2B - Autonomic toxicity mushrooms (muscarine)
Group 2C - Central nervous system toxicity mushrooms (ibotenic acid/muscimol)
Group 2D - Morel neurologic syndrome (unknown toxin)


Group 3 - Myotoxic mushroom poisoning
Group 3A - Rapid onset myotoxicity (? carboxylic acid)
Group 3B - Delayed onset myotoxicity (? saponaceolide B)


Group 4 - Metabolic/endocrine toxicity mushroom poisoning
Group 4A - GABA-blocking mushroom poisoning (gyromitrin)
Group 4B - Disulfiram-like mushroom poisoning (coprine)


Group 6 - Miscellaneous adverse reactions to mushrooms
Group 6B - Erythromelalgia-like mushroom poisoning (acromelic acid)
Group 6D - Encephalopathy syndrome (? hydrocyanic [prussic] acid)

Gummin and colleagues, 2020 (13)


Group 2 Muscimol (Ibotenic acid)
Group 3 Monomethylhydrazine (gyromitrin)
Group 4 muscarine and histamine
Group 5 Coprine
Group 6 Hallucinogenics (psilocybin and psilocin)


*Note: Not included here are categories for (1) isolated gastrointestinal symptoms (probably multiple different toxins); (2) hepatic toxicity (eg, cyclopeptide amatoxins); or (3) nephrotoxicity (eg, orellanine or orellanin).

Table 2. Comparison of Classifications of Mushroom Poisoning

Phylum

Toxidrome

Type of Mushroom

Toxin

Classification System





Barbato, 1993 (01)

Blackman, 1994 (06)

White and colleagues, 2019 (21)

Gummin and colleagues, 2020 (13)

Basidiomycota

Hallucinogenic

Psilocybe spp.

Psilocybin/psillocin

C

6

2A

6



Gymnopilus spp.








Inocybe spp.








Panaeolus spp.








Pholiotina spp.








Pluteus spp.








Amanita spp.

Muscimol/ibotenic acid

D

5

2C

2


Encephalopathic

Pleurocybella porrigens

Pleurocybellaziridine



6D



Autonomic (cholinergic)

Clitocybe and Inocybe spp.

Muscarine

B

4

2B

4


Erythromelalgia

Clitocybe spp.

Acromelic acid



6B



Disulfiram-like reaction

Coprinus atramentarius

Coprine

F

3

4B

5



Echinoderma asperum







Myotoxic (rhabdomyolysis)

Tricholoma equestre

Unknown



3B




Russula subnigricans

Cycloprop-2-ene carboxylic acid



3A


Ascomycota

Encephalopathic

Morchella spp. (Morel)

Unknown



2D



Encephalopathic (confusion and intractable seizures)

Gyromitra esculenta (False morel)

Gyromitrin/monomethylhydrazine


2

4A

3

Whites classification is the most detailed but makes some inadequately supported conclusions as well as several idiosyncratic organizational decisions (eg, the locations within the classification system of groups 4A, 6B, and 6D) (21). White incorrectly specified the toxin for Tricholoma equestre mushroom poisoning as saponaceolide B, when that toxin was identified in a related species, T. terreum, but not in T. equestre. Further, White considered T. equestre poisoning as delayed, when instead it appeared to require cumulative ingestions on several consequtive days, rather than a delayed response to a single ingestion.

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