Researchers evaluated 4 English Springer Spaniels and 3 English Cocker Spaniels with clinically confirmed episodes of exercise-induced generalized myotonic-like muscle stiffness.

Review of records confirmed that all dogs were older than 24 months at time of onset of clinical signs. The episodes of myotonic-like muscle stiffness occurred with exercise and resolved with rest within 45 seconds in six of the seven dogs.

Complete blood count, serum biochemistry including electrolytes, urinalysis, brain magnetic resonance imaging, cerebrospinal fluid analysis, electromyography, motor nerve conduction velocity, ECG, and echocardiography were within normal limits.

Muscle biopsy samples showed moderate, nonspecific muscle atrophy. The episodes seemed to remain stable or decrease in severity and frequency in 6/7 dogs, especially when avoiding triggers.

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Paradoxical pseudomyotonia in English Springer and Cocker Spaniels.