43. Diseases of the neuromuscular junction. Toxicosis, tetanus, botulism Flashcards
Included in the neuromuscular Junction and General clinical signs?
Included in the neuromuscular junction (NMJ):
§ Axon terminal
§ Synaptic cleft
§ Endplate (skeletal muscle)
Diseases Of the Neuromuscular Junction
GENERAL CLINICAL SIGNS
§ Autonomic signs § Tetraplegia
§ ↓ Muscle tone § Weakness
§ ↓ Segmental spinal reflexes § Tetraplasia
§ Cranial nerve deficits
Pre- synaptic disorders?
PRE-SYNAPTIC DISORDERS
Whereby less acetylcholine (ACh) is released from the terminal
LMN-type deficits
E.g., Botulism (see later); Tick paralysis
Clinical signs
§ Hypotonia § Dysphagia
§ Hyporeflexia § Dysphonia
Post Synaptic disorders?
POST-SYNAPTIC DISORDERS
Problems related to acetylcholine specifically
Exercise-induced weakness
E.g., Myasthenia gravis
Myasthenia gravis
Acquired form > Congenital form
Acquired: Autoantibodies produced against ACh receptors on
the post-synaptic terminal → ↓ No. functional receptors
Congenital: ACh receptor deficiency/abnormality on the postsynaptic membrane of the NMJ
Forms:
§ Generalised MG: Normal at rest; Exercise induced
weakness; Paresis; Megaoesophagus; Ptyalism
§ Focal MG: Weakness of an isolated muscle group
§ Fulminant MG: Progressive symptoms → Tetraparesis;
Diffuse weakness
Diagnosis:
§ Tensilon test
§ ACh-Rez Ab: Determines ACh receptor antibodies
§ Elecrodiagnostics
Enzymatic disorders and exercise induced collapse of labradors?
ENZYMATIC DISORDERS
Acetylcholinesterase inhibitors
Vegetative overstimulation
E.g., Organophosphate or carbamate toxicosis
Clinical signs
§ Exercise intolerance § Stiff gait
§ Muscle tremor
EXERCISE-INDUCED COLLAPSE OF LABRADORS
Similar symptoms to myasthenia gravis
After prolonged activity → Overheat → Fatigue; Flaccid paresis
Diagnosis: Genetic testing
Toxicosis?
Toxicosis
ORGANOPHOSPHATE & CARBAMATE
Found in insecticides (e.g flea collars)
Inactivation of acetylcholinesterase
Clinical signs
§ Salivation
§ Lacrimation
§ Bradycardia
Treatment: Atropine; Pralidoxime
STRYCHININE POISONING
Glycine antagonist
Clinical signs
§ Drawn-together ears § Opisthotonos
§ Sawhorse position (Fig 44.1) § Seizures
§ Hypersensitivity § Apnoea
IVERMECTIN TOXICOSIS
GABA agonist
Predisposed: Collies
Clinical signs
§ Salivation § Bradycardia
§ Mydriasis § Ataxia
§ Vomiting § Seizures
§ Tremors
Treatment: Symptomatic
LEAD TOXICOSIS
Clinical signs
§ Lethargy § GI symptoms
§ Inappetence § Depression
§ Weight loss § Seizures
§ Haematologic alterations § Ataxia
§ Blindness § Anorexia
§ Myoclonus § Hysteria
Diagnosis: Measurement of Pb in blood, urine, liver & kidney
Treatment
§ Early: Removal of lead product
§ Ca-EDTA IV
§ Sedative; Anticonvulsant
§ Diuretics
§ Short-acting glucocorticoids
OTHER TOXICOSES
§ Metaldehyde toxicosis
§ Pyethrins (cat)
§ Ethylene glycol (see topic 36)
Tetanus?
Tetanus
Clostridium tetani; Infection when the bacterium enters a wound →
Anaerobic environment → ↑ Neurotoxin production
Neurotoxin → Inhibits glycine & GABA release (inhibitory
neurotransmitter) → Spasm
Forms: Focal tetanus; Generalised tetanus
CLINICAL SIGNS
§ Extensor rigidity (Fig 44.1) § Salivation
§ Rictus grin (Fig 44.1) § ↑ Muscle tone
§ Dysphagia § Muscle spasm
§ Respiratory muscle spasm § Tachypnoea
§ Dyspnoea
TREATMENT
§ Wound debridement
§ Tetanus antitoxin
§ Abx: Penicillin; Metronidazole; Tetracycline
§ Muscle relaxant: ACP; Diazepam
§ Nutrient support; Quiet environment; Bladder expression
Botulism?
Botulism
Clostridium botulinum
Uncooked meat; Rotten carcasses; Spoiled feed
Toxin irreversibly cleaves the protein that docks ACh to the
presynaptic membrane → ↓ ACh
CLINICAL SIGNS
§ Acute paresis § Dysphonia
§ Facial paralysis § Ileus*
§ Tachycardia* § Mydriasis*
§ Bradycardia* § Dry eye*
§ Urinary retention* § Dysphagia
§ Megaoesophagus* § Death
§ Flaccid Paralysis
*Autonomic signs
DIAGNOSIS
§ History; CSx
§ Toxin detection – Mouse inoculation from serum, gastric
juice or faeces
TREATMENT
§ Emetic – Apomorphine
§ Supportive care
§ Abx are not indicated as this isn’t classed as infection
§ Antitoxin: Only works for circulating toxins
§ Prognosis: Fair/good
