CREATINE KINASE (CK OR CPK)
   Increased CK is seen with:
       Trauma
       Inflammatory muscle disease (myositis)
       Muscle necrosis (necrotizing myopathy)
       Muscular dystrophies including dystrophin, sarcoglycan, and
       laminin alpha 2 deficiency
       Cats with anorexia can have CK increases up to 20,000

An elevated CK is not diagnostic of polymyositis and a normal CK does not rule out polymyositis. A persistently elevated CK or muscle atrophy are indications for a muscle biopsy. A muscle biopsy is critical to the diagnosis of a muscle disease.

LACTATE
Need gray top tube (sodium fluoride) to measure lactate levels. Should be part of a minimum data base for dogs with exercise intolerance or muscle weakness in which a specific cause has not been determined. Inborn metabolic errors resulting in nervous system dysfunction can be associated with lactic acidemias.

PYRUVATE
In conjunction with measure of plasma lactate concentration, determination of lactate to pyruvate ratio is a good measure of oxidative metabolism. This requires special collection procedures including collection of blood into 8% perchloric acid (available from the Comparative Neuromuscular Laboratory at UCSD; http://medicine.ucsd.edu/vet_neuromuscular).

EXERCISE-INDUCED MYOPATHIES
This condition affects primarily Labrador retrievers but similar conditions have been identified in small numbers of Border collies and Golden retrievers. At least in the Labradors, this condition is thought to be a central nervous system problem and not a neuromuscular disease. Following strenuous exercise and excitement, dogs look disoriented, have ataxia rather than weakness, and routinely lose patellar reflexes during an episode of collapse. Following 20-30 minutes of rest, the dogs return to a normal clinical condition. The only treatment for this situation is exercise restriction. Exercise challenges are not recommended for these cases because some of these dogs can arrest and die if pushed too hard.

RECENTLY DESCRIBED NEUROPATHY
Leonberger dogs have an inherited peripheral neuropathy. Although not yet proven, pedigree analysis suggested that this is an X-linked inheritance pattern (Shelton et al, 2003).