It's simple, myopathy is the name for muscle diseases.

There are many subtypes of muscle diseases like ion channel diseases, metabolic deseases, ... ,or MUSCULAR DYSTROPHIES.

Muscular dystrophies are characterised by muscle fibers degeneration (degeneration/regeneration cycles)

See the "Types of Neuromuscular Disorders" section of www.muscle.ca for simple information about the myopathies.

Hope this will help

Olivier's answer above is formally correct. There are, however, a some marginal diseases, like myotonic dystrophy, where muscle degeneration/regeneration is not a major feature.

Thank you all for your input.

I was trying to figure out something along the lines of what Behzad described.

The Davies&Nowak 2006 had the closest thing to a definition but still a lot of exceptions apply.

I was just wondering if a new disease is identified what classifies it as a dystrophy (DMD/BMD, FHSD, etc) or a myopathy (Congenital, nemaline, etc)

the very difference between "myopathy and myopatic dystrophy is the NECROSIS of muscular fibers in this last one; it's enough to  apply one ematossilyn colour or Gomory's modified color to show  the fundamental difference on muscular biopsies. Today the channelmyopathies or the membrane 's proteins  defects don't change  these  cardinal points.

Though myopathy is a term indeed used in general for muscle disease, this is an oversimplification and the two terms should be used separately. The best example is the different disease groups of inherited/congenital muscle dystrophies and inherited/congenital myopathies, with all four groups consisting of different disorders. The very point of dichotomy between muscle dystrophies and myopathies (apart from dystrophic/necrotic features (usually) not present in myopathies) is that dystrophies are linked to (genetic) alterations in membrane/structural elements, whereas myopathies are linked to alterations in contractile elements of the muscle fibers. See: Semin Neurol. 2008 Apr;28(2):250-9. doi: 10.1055/s-2008-1062269

There is a danger here of arguing about definitions when what matters from a scientific viewpoint is mechanisms. The term myopathy, can be applied to any muscle disease. The term dystrophy was classically applied by pathologists to the subset of inherited myopathies in which muscle tissue destruction was a major feature. For some reason myotonic dystrophy became aberrantly included in this category. Myositides contain a myonecrotic element but were not thought to be genet although it is becoming realized that there may be a genetic element to some of them. We must revise our taxonomy with increasing knowledge although some people find this inconvenient.