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Causes of Neuromuscular Weakness in Dogs

JP McCue, DVM, DACVIM (SAIM & Neurology), The Animal Medical Center, New York, New York

Neurology

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May 2022
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Peer Reviewed

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Causes of Neuromuscular Weakness in Dogs

This interactive article reviews clinical features that can help identify and distinguish common causes of neuromuscular weakness.


Introduction

Localizing the cause of weakness in the neuromuscular system can be challenging. Diagnosis requires careful examination and analysis of patient history and clinical sign progression.

Neuromuscular disorders generally reflect disease of the lower motor neuron unit. Sensory function remains intact in most cases. Different diseases affecting the lower motor neuron unit can cause similar clinical signs (Table 1), including decreased muscle tone, reduced reflexes, and muscle atrophy. Autonomic signs and cranial nerve deficits can be present with generalized muscle weakness. Pattern recognition can help determine the most likely differential diagnosis, as well as appropriate diagnostic testing and treatment.

Table 1

SUMMARY OF CLINICAL SIGNS

Disease Reflexes Cranial Nerve Abnormalities Hyperesthesia CSF Autonomic Signs Onset of Weakness
Myasthenia gravis Intact Megaesophagus, facial paresis, dysphonia None Normal None Exertional weakness
Tick paralysis Decreased Dysphonia None Normal None Rapid, diffuse lower motor neuron weakness
Polyradiculoneuritis Decreased Dysphonia, facial paresis Occasional spine, distal limbs Increased protein with normal cell count None Ascending weakness (hours to days), tail wag intact
Botulism Decreased Dysphonia, megaesophagus, facial paresis None Normal Mydriasis, ileus, ptyalism, decreased bladder tone Rapid, diffuse lower motor neuron weakness
Polymyositis Intact or decreased Dysphagia, decreased swallowing Possible myalgia Normal None Focal or diffuse weakness with variable onset

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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