Suspected muscarinic mushroom intoxication in a cat

Abstract

A 3-year-old domestic shorthair cat was witnessed ingesting mushrooms and developed signs of muscarine intoxication. After stabilisation and treatment with atropine the cat recovered well and was discharged from hospital in 2 days. This report describes the features and successful management of this unusual toxicosis in cats.

Case Report

A 3-year-old, male neutered, domestic shorthair cat presented to the emergency service for an acute episode of dyspnoea, cyanosis, open-mouth breathing and drooling. In less than 30 mins following the witnessed ingestion of mushrooms, the cat had started drooling, and then vomited mushrooms and passed diarrhoea. This was followed minutes later by the onset of respiratory distress. No other significant history was reported. On examination of the major body systems (primary survey) significant abnormalities detected were moderate-to-severe bradycardia [heart rate (HR) 100 beats per min], poor quality pulses, tachypnoea [respiratory rate (RR) 92 breaths per min] with open-mouth breathing, bilateral pulmonary crackles, depressed mentation and severe bilateral miosis (Figure 1). An emergency database was obtained consisting of manual packed cell volume (PCV), plasma total solids (TS), venous blood gases and electrolytes, and plasma biochemistry profile. The following significant findings were detected: PCV 59%, TS 10.2 g/l, glucose 14.5 mmol/l [reference interval (RI) 3.5–7.5 mmol/l], urea 15.5 mmol/l (RI 2.8–11 mmol/l) and creatinine 167 μmol/l (RI 0–190 µmol/l). Venous blood gases, electrolytes and liver transaminases (alanine aminotransferase and alkaline phosphatase) were within RIs. These findings were considered consistent with haemoconcentration and pre-renal azotaemia, most likely secondary to hypersalivation and gastrointestinal fluid loss. The mild hyperglycaemia was presumed to be ‘stress’-induced. Given the severity of the cat’s dyspnoea and associated crackles, empirical furosemide (Dimazon; Intervet) at a dose of 3 mg/kg was administered intramuscularly and the cat was then placed in an oxygen cage with close monitoring. After a few minutes breathing had improved sufficiently for a more comprehensive physical examination (secondary survey) to be completed on which no other significant abnormalities were detected. The history of mushroom ingestion and the associated clinical findings were considered suggestive of muscarinic intoxication. Atropine (Hameln Pharmaceuticals) was therefore given by intramuscular injection at a dose of 0.04 mg/kg, to which a positive response was witnessed within 30 mins. Repeated major systems examination revealed a HR of 200 beats per min, a RR of 40 breaths per min with mild residual crackles and improved mentation. Intravenous fluid therapy was started with Hartmann’s solution at 6 ml/kg/h. Some gastrointestinal decontamination had occurred via vomiting and it was not considered rational to attempt activated charcoal administration given the unpredictability of the cat’s clinical status going forward. The cat improved gradually without any further medication and was discharged 2 days following initial presentation.

Figure 1

Cat showing severe miosis

Mushroom toxicity is uncommon in cats. The Veterinary Poisons Information Service in the UK has received 867 canine and only 57 feline enquiries relating to potential mushroom exposure over the last 10 years. ¹ Similarly, the Animal Poison Control Center in the USA receives, on average, six feline reports annually. ² The most common mushrooms involved in muscarine poisoning include the genera Inocybe and Clitocybe, although the genera Mycena, Boletus, Entoloma and Omphalotus can have significant muscarine levels. ² Unfortunately, it was not possible to accurately identify the mushrooms ingested in this case. Correct morphological identification of mushrooms can be challenging and, if in doubt, it is recommended that a mycologist is consulted for complete identification using the fungal spores; samples should be stored wrapped in paper rather than plastic bags or containers, as the latter can result in sample deterioration due to high humidity. Muscarine is a muscarinic receptor agonist that produces postganglionic parasympathomimetic effects. ² Signs of intoxication can occur rapidly (within 5–30 mins) and mostly within 2 h of ingestion, and may include one or more components of salivation, lacrimation, urination and diarrhoea (SLUD). ³ Other common clinical signs include bradycardia, hypotension, shock, dyspnoea and wheezing due to bronchoconstriction and increased respiratory secretions, abdominal pain, miosis, visual disturbance and rhinorrhoea. As a result, another, more comprehensive, acronym used is DUMBBELS (diarrhoea, urination, miosis, bronchorrhoea, bronchoconstriction, emesis, lacrimation, salivation). ³ The cat described in this case was presented with most of these signs, showing diarrhoea, emesis, salivation, miosis, and signs of bronchorrhoea and bronchoconstriction. The rapid onset of signs following witnessed mushroom ingestion also suggests muscarinic intoxication. Other possible aetiologies to consider in the differential diagnosis are exposures to organophosphates and carbamates. ² These pesticides act by inhibiting acetylcholinesterase causing parasympathomimetic effects similar to muscarine intoxication; however, they also stimulate nicotinic receptors and cross the blood–brain barrier producing nicotinic signs, such as muscle tremors and seizures. ² The recommended therapy for muscarine intoxication includes gastrointestinal decontamination, antidotal atropine administration, oxygen supplementation and supportive measures, such as fluid therapy.^2,3 Atropine competes with muscarine at the level of the receptors. Literature guidelines for atropine therapy vary considerably with respect to the dose and route of administration.^{2 –4} Doses reported for its use in muscarine intoxication vary between 0.04 mg/kg and 2 mg/kg.^2,3 The dose used in this case was therefore the lowest recommended dose, but a satisfactory response was seen within 30 mins, which is similar to other published reports in small animals. ² Most publications recommend giving part of the dose intravenously and part either subcutaneously or intramusculary.^2–4 In this case we decided to administer the full dose intramuscularly to avoid excessive handling in a dyspnoeic patient and the effect was satisfactory. A recommended clinical end-point to guide atropine therapy is the drying up of oral and respiratory secretions. ³ It is recommended not to use the resolution of miosis for this purpose because by the time the pupils return to normal size most patients are likely to have received too much atropine. ³ Potential adverse effects of excessive atropinisation include tachycardia, hyperthermia, behavioural changes and gastrointestinal stasis.^2,4

Conclusions

This report describes the features and successful management of suspected muscarinic mushroom intoxication in a cat, and shows that this unusual toxicosis can be managed successfully in this species. To our knowledge this is the first published report of suspected muscarinic mushroom intoxication in cats. The cat described in this case responded well to appropriate therapy and did not show any long-term effects, which is similar to other published reports in dogs. ²