Hypertonicity or Episodic Falling, also known as Hyperkinesis, Falling Cavaliers, Collapsing Cavalier Syndrome, Scotty Cramp or Paroxysmal Hypertonicity Disorder, is characterized by episodic, paroxysmal attacks during which affected animals fall, exhibit muscle rigidity and may be acutely and dramatically incapacitated. Dogs do not lose consciousness and are clinically normal between attacks. Episodes appear to be triggered by stress, apprehension, and excitement, where affected animals develop a peculiar bounding, pelvic limb gait in which the limbs may be abducted and appear stiff.
Episodic Falling is a syndrome of muscle stiffness and collapse, with the pathophysiology considered to involve abnormal neurotransmitter function. However, microscopic changes are often not observed within the central nervous system.
Age at onset: Dogs typically present with symptoms between 3 and 7 months of age. Puppies as young as 12 weeks of age have shown symptoms; episodes present throughout an affected dog's lifespan.
Symptoms: Dogs collapse without loss of consciousness and display limb rigidity.
Genetics of Episodic Falling: Research studies indicate that Episodic Falling is an inherited trait in the Cavalier King Charles Spaniel breed. Genetic mutations linked to both Episodic Falling and Dry eye and curley coat syndrome (known as congenital keratoconjunctivitis sicca and ichthyosiform dermatosis) have been identified. This lead to the development of DNA tests to identify carriers. These DNA tests were made available in April 2011 from the Animal Health Trust.
Episodic Falling in Humans: It has been suggested that this disorder has some similarities to hyperexplexia (startle disease) in people, a hereditary (autosomal dominant) pathological exaggeration of the normal startle response to auditory, somesthetic or visual stimuli which sometimes results in falling.
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