Web-Vet TM Neurology Specialists
Myotonia and Myoclonus
Myotonia is defined as delayed muscle relaxation after muscle activation, usually preceded by a period of rest, and improving with continuous activity (warm-up phenomenon).
Myoclonus is defined as a brief, shock‐ or jerk-like movement secondary to involuntary muscle contraction or relaxation. It can be hyperkinetic which manifests as a jerking muscle contraction, or hypokinetic where there can be loss of muscle tone resulting in stumbling or falling.
Myoclonus in older Cavalier King Charles Spaniels
The aim of this retrospective study was to document the characteristics and treatment of myoclonic episodes in a cohort of CKCS.
Thirteen of 39 dogs with myoclonus had paroxysmal events, such as generalized seizures (9/13). Clinical signs were spontaneous in onset, lasted a few seconds and consisted of rapid blinking with head nodding and variable extension down the thoracic limbs. Myoclonus occasionally led to stumbling of the thoracic limbs or collapse. Mean age of onset was 8.38 years.
An example of this is shown in the video of one of our previous patients below.
Paradoxical pseudomyotonia in English Springer and Cocker Spaniels
This case series describes 7 dogs with clinically confirmed episodes of exercise-indccued generalised myotonic-like muscle stiffness. All episodes resolved spontaneously within <45 seconds in all but 1 dog. Thorough investigations performed only showed moderate but non-specific muscle atrophy on muscle biopsy samples. Episodes could often be decreased or eliminated by avoiding episode triggers. The genetic variant responsible for this disorder in Spaniels currently remains unknown. We are grateful to the first author of this paper Kimberley Stee for providing this video.
Characteristics and clinical course of myoclonus in Cavalier King Charles Spaniels
The aim of this study was to report the clinical features and course of myoclonus in CKCS.
Most of the 27 included CKCS displayed spontaneous myoclonus affecting predominantly the head (25/27). Overall, the majority had episodes that increased in frequency (20/27) and severity (17/27). Eighteen dogs had developed changes in behavior since the onset of myoclonus. These dogs were typically older and had experienced myoclonic episodes for longer than dogs without behavioral changes. Generalized epileptic seizures were reported in 4/27 dogs. Ten dogs received medical treatment. Eight were prescribed levetiracetam; all had an initial decrease in episode frequency, but a subsequent increase in both frequency and severity of episodes was common.
An example of the episodes is shown in this video which was included in the authors' paper.