April 11, 2011 at 11:53 am

The differences, as I read about them, seem to focus on a determination of the rapidity, acuteness (right now) and duration of the symptoms. Read about this from Johns Hopkins-

GBS patients develop rapidly progressive sensory symptoms such as unusual sensations (paresthesias) and numbness, and motor symptoms such as weakness and cramping in their legs followed by their arms. Patients may also develop weakness of their breathing and difficulty chewing and swallowing. Difficulty breathing may create a neurological emergency as the patients can develop respiratory arrest. A sizeable number of patients also develop autonomic dysfunction where they experience fluctuations in their blood pressure and cardiac arrhythmias. GBS is one of the true neurological emergencies. Patients need to be monitored closely during the initial acute phase of the illness. In contrast, CIDP is a slowly progressive illness with diffuse sensory and motor symptoms.[/I]

From Neurology. 2010 May 25;74(21):1680-6. Epub 2010 Apr 28.

“[I]CONCLUSIONS: The diagnosis of acute-onset chronic inflammatory demyelinating polyneuropathy (CIDP) should be considered when a patient thought to have Guillain-Barré syndrome deteriorates again after 8 weeks from onset or when deterioration occurs 3 times or more. Especially when the patient remains able to walk independently and has no cranial nerve dysfunction or electrophysiologic features likely to be compatible with CIDP, maintenance treatment for CIDP should be considered.[/I]”

So, it would seem, you may very well have Acute (right now) symptoms and be diagnosed with CIDP, not GBS due to the symptoms lasting, or worsening after the 8 week period. I have read repeatedly that the 8 week number could be used as a guideline, or cut-off in decision making.

Also, it sounds as if there are EMG/NCV differences. However, I do not know what those differences are.