From Dr. Waclawik:
A small percentage of patients with CIDP may have an acute onset and a rapidly progressive deficit. Those cases may be indistinguishable from AIDP/GBS and only careful follow up with periodic reassessment (clinical and electrophysiological) can allow us to classify a specific case. Some patients with GBS/AIDP may have some fluctuations of the initial clinical course but they still represent a monophasic condition, although frequently with slow, protracted recovery (and residual neurological deficits). The distinction between AIDP vs. SIDP vs. CIDP in some cases may not be straightforward, especially at the time of the initial encounter. One can make some analogy to the cases of TIA vs. stroke when they are seen acutely in the ER. The time course and evolution/ recovery/progression of the deficits help us to correctly classify many neurological conditions. With regard to the current case, it is very interesting. Most of the paraneoplastic polyneuropathies are axonopathies, with predominately sensory involvement. However, association of CIDP with different malignancies has been well recognized in the literature.
I think the general point about the importance of time course is worth emphasizing. Time is a critical dimension in assigning an etiological diagnosis, whether it be AIDP vs CIDP as in the present case or MS vs. ADEM as was discussed at CNS conference today (nice job, Matt). In my own practice, I’ve seen countless patients in stroke clinic for “TIA” whose time course made that a clearly untenable diagnosis. If someone tells you they’ve had 150 TIAs over a 20 year period, the diagnosis is almost certainly not TIA. If someone has a spell of focal neurological dysfunction that slowly spreads from one part of the body to another, then migraine becomes an important consideration, etc. These are fairly obvious examples that you’re all aware of, but I think it’s helpful when tackling a challenging case to think explicitly–“system 2” thinking in Kahneman’s parlance–about time course.