Myotonia is a genetic muscle disorder characterized by slow relaxation of skeletal muscles. Signs include: stiff gait, skeletal muscle hypertrophy, difficulty swallowing, difficulty standing up/rising, increased respiratory sounds, generalised stiffness, and increased salivation. Age of onset 2-3 months of age. Signs can vary somewhat by breed/type.
Heritable myotonia is a genetic muscle disorder characterized by slow relaxation of skeletal muscles. The main clinical signs are skeletal muscle stiffness, especially after vigorous contraction, and muscle hypertrophy. Muscle stiffness may be enhanced by inactivity, and often is relieved by exercise. (From Finnigan et al, 2007)
Finnigan, DF., Hanna, WJ., Poma, R., Bendall, AJ. : A novel mutation of the CLCN1 gene associated with myotonia hereditaria in an Australian cattle dog. J Vet Intern Med 21:458-63, 2007. Pubmed reference: 17552451.