Disorders of peripheral nerves, neuromuscular junction and muscles

Question 1

What would be your differentials for weakness in cats

Answer 1

Primary polyneuropathy

Primary polymyopathy

Junctionopathy

Cardiovascular problems
- decreased cardiac output due to cardiomyopathy, arrhythmias, valvular disease, ….
- conditions leading to hypoxia (e.g., severe lung disease, anemia)
- polycythemia
- hypovolemia/hypoperfusion

Metabolic disorders
- hypoglycemia
- hypokalemia
- hypo/hypercalcemia
- hypo/hypernatremia
- other severe disorders (e.g., uremia, hepatopathy, sepsis, …)

Question 2

What are the typical clinical signs for neuromuscular weakness

Answer 2

Generally, cats with disease at the level of the motor unit (i.e., nerve, neuromuscular junction, muscle fibers) have normal mentation, unless suffering from concomitant metabolic or central nervous system disease

Neuromuscular weakness is often manifested as passive ventroflexion of the head

The gait is generally not ataxic, but the patient may be reluctant to ambulate and may frequently lie in sternal recumbency, often with the head resting on the front legs
- the gait is stilted and short striding and the head may nod in time with the steps

Poor withdrawal reflexes are another hallmark of peripheral weakness

Question 3

What is the difference between a peripheral nerve disorder and a myopathic disorder

Answer 3

In disorders affecting the peripheral nerves, hyporeflexia of the spinal nerves is frequently observed

Generally, cats with myopathic disorders have intact spinal reflexes, unless severely affected

Question 4

Which laboratory exam could help discriminate neurological disorders from myopathic disorders

Answer 4

Creatine kinase may be increased with myopathies
- normal values do not rule muscular disease out

Question 5

What investigation is prudent to include in older cats presented for weakness

Answer 5

In older cats, it may be prudent to include thoracic radiography and abdominal ultrasonography as part of the initial evaluation
- to investigate the presence of concurrent disorders
- to rule out neoplastic conditions that may be the primary cause of the problem (e.g., paraneoplastic polyneuropathies, thymoma-induced myasthenia gravis)