The term “tremorgenic” describes any substance that can produce tremors, which are involuntary, rhythmic muscle contractions. These substances are neurotoxins, meaning they affect the nervous system to induce these uncontrolled movements. While the term can apply to various compounds, it is most frequently used for specific natural toxins that can be harmful to both animals and humans.
Common Tremorgenic Substances
The most frequently encountered tremorgenic substances are mycotoxins, which are toxic compounds produced by fungi or mold. At least 20 different mycotoxins have tremor-inducing capabilities, but only a few are commonly involved in clinical poisoning cases. Among the most significant are Penitrem A and Roquefortine C, produced by Penicillium molds. These molds grow on decomposing organic materials like moldy bread, spoiled dairy products, and nuts. Dogs are particularly susceptible due to their indiscriminate eating habits, making ingestion of moldy food from garbage or compost a frequent route of exposure.
While mycotoxins are the primary concern, other substances can also induce tremors. Certain industrial chemicals, like cholinesterase inhibitors found in some pesticides, can have tremorgenic effects. Additionally, some illicit drugs, such as amphetamines, and certain medications like pseudoephedrine, can stimulate the central nervous system and lead to similar signs. However, poisoning from moldy food remains the most common scenario.
How Tremorgenic Substances Affect the Body
Tremorgenic substances exert their effects by directly interfering with the central nervous system’s communication channels. Their primary action is to disrupt the function of inhibitory neurotransmitters, which are chemicals nerve cells use to reduce neural activity and prevent excessive firing. This disruption leads to a state of over-excitation within the nervous system, manifesting as uncontrolled muscle movements.
Specifically, many tremorgenic mycotoxins impair the signaling of gamma-aminobutyric acid (GABA) and glycine. These two neurotransmitters are the main inhibitory agents in the brain and spinal cord, functioning like a braking system for the body’s muscles to allow for controlled, coordinated movement.
When toxins enter the body, they block the receptors for GABA and glycine. Without these inhibitory signals to counteract excitatory ones, nerve cells fire erratically and excessively, resulting in the continuous muscle contractions observed as tremors.
Signs of Tremorgenic Toxin Exposure
The signs of exposure to a tremorgenic toxin appear rapidly, often within one to two hours of ingestion. The initial presentation often involves fine, subtle muscle twitching, which may resemble shivering. As the toxin’s effects progress, these minor twitches can escalate into more severe, whole-body tremors that are readily apparent. Vomiting may also occur before the tremors begin.
With increased severity, the tremors can become so intense that they interfere with the ability to stand or walk, leading to a lack of coordination known as ataxia. An affected animal may appear agitated and restless.
In serious cases, persistent muscle contractions can lead to a dangerous increase in body temperature, a condition called hyperthermia. The most severe exposures can result in seizures, which can be life-threatening if not managed. These signs can persist for hours or even days depending on the amount of toxin ingested.
Medical Diagnosis and Management
A diagnosis of tremorgenic poisoning is most often based on the observable clinical signs, such as tremors and seizures, combined with a recent history of potential exposure. For instance, a veterinarian may suspect mycotoxin ingestion if a dog owner reports that their pet was recently seen eating from a garbage can or compost pile. While specialized laboratory tests can identify specific tremorgens, treatment is initiated based on the strong presumptive diagnosis from the history and physical examination.
The immediate goal of medical management is to decontaminate the patient to prevent further absorption of the toxin. This may involve inducing vomiting, if the ingestion was recent and the patient is stable, or administering activated charcoal. Activated charcoal works by binding to the toxins within the gastrointestinal tract, preventing them from entering the bloodstream.
Following decontamination, treatment focuses on supportive and symptomatic care. Intravenous (IV) fluids are often administered to maintain hydration and support organ function. Muscle relaxants and anti-seizure medications are administered to calm the tremors and stop seizures.
With prompt and aggressive treatment to manage the symptoms, the prognosis is generally good, and most patients recover without long-term effects.