43. Diseases of the neuromuscular junction. Toxicosis, tetanus, botulism Flashcards

1
Q

Included in the neuromuscular Junction and General clinical signs?

A

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

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2
Q

Pre- synaptic disorders?

A

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

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3
Q

Post Synaptic disorders?

A

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

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4
Q

Enzymatic disorders and exercise induced collapse of labradors?

A

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

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5
Q

Toxicosis?

A

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)

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6
Q

Tetanus?

A

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

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7
Q

Botulism?

A

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

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