Most of the neuromuscular fellowships are neuro based UC Davis being the notable exception. This is their first year accredited, if Im not mistaken. Most of these fellowships obviously favor neuro grads over PM&R (wonder if UC Davis will look at neuro applicants?), although theres probably the rare exception floating around. Heard from a reliable source that the Harvard/MG/BWH neuromuscular fellowship accepted their first PM&R resident for next year.
There are a few ACGME accredited clinical neurophysiology (EMG) fellowships OTOH, that have occasionally taken PM&R residents. But it depends on the individual institution, and it seems like they tend to favor their own residents. Physiatrists arent eligible to sit for the clinical neurophysiology boards. And - someone correct me if I'm wrong - none of these clinical neurophys/EMG fellows will be able to sit for the neuromuscular boards in the future.
The 2012 exam is the last time to get grandfathered in for neuromuscular medicine. Im still debating whether or not its personally worth it. Its meaningless to me now in my established practice (which is probably why the OSU/Mayo docs wont do it), but it would come in handy in the future if I ever decide to move.