Myokymia and neuromyotonia in 37 Jack Russell terriers

The novel homozygous KCNJ10 c.986T>C (p.(Leu329Pro)) variant is pathogenic for the SeSAME/EAST homologue in Malinois dogs

“…Urinalysis (including electrolyte clearance for Na + , K + , Cl -, Ca 2+ , Mg 2+ and PO 4-), was unremarkable in dog 3. EMG showed neuromyotonic discharges 5,33 in those muscles also visibly showing myokymia in dogs 1 and 2 ( Figure 3), and was normal in dog 3. BAER recordings showed disappearance of wave components III/IV and V, and mildly prolonged latencies of waves I and II in dogs 1 to 3 ( Figure 4).…”

“…The authors do not believe that systemic electrolyte disturbances would have resulted in myokymia and neuromyotonia in the affected Malinois dogs, as serum electrolytes and electrolyte clearance were normal. The fact that all dogs had ataxia, but only some dogs had seizures, myokymia or neuromyotonia, is not surprising, as it is well known that potassium channel diseases can be phenotypically heterogeneous (variability of clinical signs and severity) in dogs 33 and humans. 1,2,43 The mildly delayed latencies of waves I and II, and the loss of waves III, IV and V, was repetitively found on the BAER tests of our affected dogs.…”

“…47 In Jack Russel Terriers, the ataxia also seems to be nonprogressive, but the myokymia and neuromyotonia worsen gradually over several months, leading to killing of most dogs. 33 Because of the larger stature of Malinois dogs compared with Jack Russell Terriers, they seemed to cope less easily with the ataxia during growth of the animal. Hence, mid-to long-term prognosis in these dogs is reserved to poor.…”

Canine Hereditary Ataxia

“…The first important phenotype is one of cerebellar ataxia combined with myokymia (rippling involuntary muscle contractions), neuromyotonia (sustained muscle contractions), and seizures. 6,42,43 Onset of ataxia is between 2 and 10 months of age and typically there is obvious progression over a few weeks, then stabilization with intermittent periods of deterioration. Dogs exhibit a hypermetric, spastic gait, with postural reaction and proprioceptive placing deficits localizing to the cervical spinal cord.…”

“…In another report, dogs developed signs of ataxia followed by myokymia and neuromyotonia. 42,43 Brainstem auditory evoked responses (BAERs) are frequently abnormal in affected dogs. Most dogs are euthanized because of the disease at a mean of 1 year after onset 6 ; although milder, more slowly progressive, phenotypes are also recognized.…”