Myoclonus in older Cavalier King Charles Spaniels

Background Myoclonus is observed in older Cavalier King Charles Spaniels (CKCS) but a full description is lacking. Objectives The presence, age of onset, characteristics and treatment of myoclonic episodes were retrospectively evaluated in a cohort of CKCS which presented to 1 board-certified neurologist. Clinical data, imaging studies, presence of seizures and their management, as well as other comorbidities were noted. Animals Thirty-nine CKCS that were presented to 2 institutions between 2001 and 2018 with signs consistent with myoclonus. Clinical examination, blood sampling, advanced diagnostic imaging, cerebrospinal fluid analysis, and record keeping of other comorbidities was performed. Methods This is a retrospective case series, describing the presence of myoclonus in CKCS. Results Clinical signs reported 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 (SD +/- 1.96). Thirteen of 39 dogs with myoclonus had paroxysmal events, such as generalized seizures (9/13). Conclusions and Clinical Importance Myoclonus occurs in middle-aged to older CKCS and seems to be another epiphenomena of this breed. A link to epilepsy might be present.