Toxic Fungi of Western North America

by Thomas J. Duffy, MD

Autoimmune hemolysis with Paxillus involutus

Raw or poorly cooked Paxillus involutus may cause severe gastrointestinal symptoms, but the red cell destruction and hemoglobin changes of severe poisoning are due to sensitization to the mushroom. Although rare exceptions have been noted, this mushroom poisoning usually reflects repeated ingestion of the mushroom over a period of years, gradually producing antibodies directed against red blood cells. Then the acute syndrome intervenes following a new ingestion of the mushroom. Most patients are elderly, reflecting the years it may take to build up sensitivity and to allow a decrease in the body’s auto-antibody defenses.

Paxillus involutus
Paxillus involutus photo © Michael Wood

There have been only two cases in the West. Janet Lindgren, chairing the Toxicology Committee of the Oregon Mycological Society, noted two cases just across the Oregon border from Portland in Vancouver, Washington. Of these two cases, one victim had some loss of vision due to central retinal necrosis. These appear to be the only North American cases. Seattle collections over a number of years—“cooked, pickled and raw”—have led to no toxicity. (142)

This medium-sized, squat, brown, rather ugly mushroom with olivaceous tints does not seem unusual at first glance except for its depressed cap and inrolled cap edges. However, on picking, it readily bruises a dark brown, which may be reddish at first, but almost immediately becomes a dingy or slightly olivaceous dark brown. The gills are striking in that they are close and run down the stipe. Like the pores in boletes, one’s thumbnail readily scoops out the gills in mass from the cap.

The cap of Paxillus involutus is dry to subviscid, dull, matted with fibrils and has a hairy margin that becomes very strongly inrolled early in its development. The color varies from a slightly yellowish to slightly rusty brown, usually with olive tones. It bruises as noted above and the crowded, deeply decurrent gills tend to fork, again suggesting the fruiting body of a bolete: one can scoop out the gills from under the cap, much as one can scoop out the tubes from boletes with their sponge-like, but more regular tube mouths. The cap is 4-12 cm across and perched on a 2-10 cm long stipe, equal or enlarged downwards. The spore print is yellow-brown. These mushrooms spring up solitary or scattered in small groups, most commonly on decaying wood near conifers in the fall. They also occur on garden paths and in mixed woods.

Eaten primarily in Europe, this mushroom usually produces only gastrointestinal symptoms, which begin in 1-4 hours. Malaise, weakness and sweating may be present. However, if autoimmune hemolysis has taken place, the clinical course may progress to changes in consciousness, cardiovascular collapse, kidney failure and other organ problems associated with autoimmune hemolysis. (143,144) A hemoagglutination test for this poisoning using cooked, freeze-dried powder from Paxillus involutus is available in Europe. (18)

A variant of the hemoagglutination test noted above can be carried out with fresh Paxillus involutus gently heated in a small amount of physiologic saline for 30 minutes. 0.2 ml of this extract is added to 0.1 ml of the patient’s serum and incubated at 37º C (98.7º F) for 30 minutes. In the next step, 0.2 ml of a 10% suspension of normal donor red blood cells is added and incubated at 37º C for 60 minutes. Then the resultant mixture is briefly centrifuged to allow examination of a more concentrated sample of red blood cells. A positive test is agglutination (clumping of red cells) under the microscope. (145)

Usually a description of eating a squat brownish mushroom (cap wider than height of stalk), a history of repeated ingestion and the occurrence of hemolysis make diagnosis a rather easy task. Laboratory abnormalities include a decreased red cell count, elevated white cell count, free hemoglobin in the serum with a corresponding fall in haptoglobin (to which it binds) and abnormal kidney function tests. Tests for standard autoantibodies are negative.

Treatment is largely directed at stabilizing the cardiovascular system, managing fluid and electrolyte requirements and reducing symptoms. Intravenous high-dose dexamethasone (an anti-inflammatory steroid) has been used to reduce the immune response, but its efficacy is not proven. Renal dialysis should be available. The best treatment for severely ill patients seems to be plasma exchange transfusion with 5% albumen. (145)