ABSTRACT: Up to 16% of chronic inflammatory demyelinating polyneuro-
pathy (CIDP) patients may present acutely. We performed a retrospective
chart review on 30 acute inflammatory demyelinating polyneuropathy (AIDP)
and 15 acute-onset CIDP (A-CIDP) patients looking for any clinical or
electrophysiological parameters that might differentiate AIDP from acutely
presenting CIDP. A-CIDP patients were significantly more likely to have
prominent sensory signs. They were significantly less likely to have
autonomic nervous system involvement, facial weakness, a preceding
infectious illness, or need for mechanical ventilation. With regard to
electrophysiological features, neither sural-sparing pattern, sensory ratio
>1, nor the presence of A-waves was different between the two groups. This
study suggests that patients presenting acutely with a demyelinating
polyneuropathy and the aforementioned clinical features should be closely
monitored as they may be more likely to have CIDP at follow-up.
Muscle Nerve 000: 000–000, 2009
CLINICAL AND ELECTROPHYSIOLOGICAL
PARAMETERS THAT DISTINGUISHING ACUTE-
ONSET CHRONIC INFLAMMATORY
DEMYELINATING POLYNEUROPATHY FROM
ACUTE INFLAMMATORY DEMYELINATING
POLYNEUROPATHY
ANNIE DIONNE, MD,1 MICHAEL W. NICOLLE, MD, DPhil,2
and ANGELIKA F. HAHN, MD2
1Department of Clinical Neurological Sciences, Universite´ Laval, 1401 18 rue,
Que´bec City, Que´bec G1J 1Z4, Canada
2Department of Clinical Neurological Sciences, University of Western Ontario,
London, Ontario, Canada
Accepted 16 June 2009
The spectrum of acquired inflammatory demyeli-
nating polyneuropathy ranges from the acute
variant, Guillain–Barre´ syndrome (GBS), to a
chronic form, chronic inflammatory demyelinating
polyneuropathy (CIDP). Although CIDP is defined
as a progressive or relapsing condition that devel-
ops over at least 2 months,1 previous studies have
shown that up to 16% of CIDP patients may pres-
ent acutely.2–6 Such patients are usually initially
diagnosed with acute inflammatory demyelinating
polyneuropathy (AIDP), but later, as they either
relapse or continue to progress beyond 2 months,
they are then correctly diagnosed as having CIDP.
An early and accurate diagnosis has major prog-
nostic and treatment implications. Unfortunately,
the diagnosis can only be confirmed with certainty
at follow-up, after a minimum of 2 months of
clinical observation. Therefore, earlier indicators,
either clinical or electrophysiological, would be
useful to guide treatment and prognostication. In
this study we retrospectively reviewed electrophysio-
logical and clinical data to determine whether any
differences would allow prediction of the subse-
quent course when patients were seen early in
their disease.
The electrodiagnostic pattern of a preserved
sural sensory nerve action potential (SNAP) with
an abnormal median SNAP has been deemed
Abbreviations: AIDP, acute inflammatory demyelinating polyneuropathy;
A-CIDP, acute-onset chronic inflammatory demyelinating polyneuropathy;
CIDP, chronic inflammatory demyelinating polyneuropathy; CSF,
cerebrospinal fluid; GBS, Guillain–Barre´ syndrome; INCAT, Inflammatory
Neuropathy Cause and Treatment Group; IVIg, intravenous
immunoglobulin; SNAP, sensory nerve action potential
Correspondence to: A. Dionne; e-mail: annie.dionne.cha@ssss.gouv.
qc.ca
V
C 2009 Wiley Periodicals, Inc.
Published online in Wiley InterScience (www.interscience.
wiley.com). DOI 10.1002/mus.21480
Key words: acute inflammatory demyelinating polyneuropathy; chronic
inflammatory demyelinating polyneuropathy; clinical predictors;
electrophysiology; sural sparing
AIDP vs. A-CIDP MUSCLE & NERVE Month 2009 1

suggestive of an acquired demyelinating polyneu-
ropathy rather than an axonal, length-dependent
process. This finding has been reported mainly in
AIDP patients and has been touted as predictive of
AIDP rather than CIDP.7–14 However, this observa-
tion has not been studied in the acute phase.
Recently, the ‘‘sensory ratio’’ [(sural þ radial)/
(ulnar þ median) SNAP amplitude] was found to
be a useful marker of AIDP.9 We reviewed electro-
physiological data from sensory nerve conduction
studies to compare these findings, as well as the
presence of A-waves on F-response studies, in
patients with AIDP and A-CIDP.
With regard to clinical parameters, prominent
motor dysfunction with mild sensory symptoms
and signs are features thought to support a diagno-
sis of GBS.15 Whether the converse, prominent
sensory signs and symptoms, is more suggestive of
CIDP is not known. We compared the sensory
signs and symptoms as well as the other clinical
features at presentation between the two groups.
METHODS
A retrospective chart review was performed on
patients with AIDP and acute-onset CIDP (A-CIDP)
assessed clinically from 1993 to 2007 by a neuro-
muscular neurologist (A.F.H., London Health
Sciences Centre, London, Ontario, Canada). Both
clinical and electrodiagnostic records were
reviewed. The study protocol was approved by the
University of Western Ontario ethics review board.
AIDP was diagnosed according to the diagnos-
tic criteria established by Asbury.15,16 Criteria
required demonstration of weakness ranging from
mild weakness of legs to complete paralysis of all
extremities and bulbar and facial muscles as well
as areflexia or definite hyporeflexia. Time from
onset to plateau of symptoms had to be <4 weeks,
and the diagnosis had to be confirmed at follow-
up: no relapse (single treatment related fluctua-
tions were permitted); no progression beyond 8
weeks; and no need for maintenance therapy.
Patients with variants of GBS (Miller–Fisher syn-
drome, other regional variants, acute motor axonal
neuropathy, and acute sensorimotor axonal poly-
neuropathy) were excluded. Patients with associ-
ated systemic disorders that might cause a neurop-
athy were also excluded, such as patients with
diabetes, hereditary neuropathies, paraproteine-
mia, and carcinoma, as well as patients with other
disorders that might influence the neurological
examination or the results of electrophysiological
studies. All patients were seen between 1 and 6
months after hospital discharge. At their follow-up
visits, they were instructed to return if they had a
recurrence of neurological symptoms. Patients who
had missed their follow-up appointments, which
were set up to confirm absence of relapse or of
continued worsening, were excluded.
A-CIDP was diagnosed when patients presented
acutely within 4 weeks of onset of symptoms and
were diagnosed initially with AIDP but continued
to progress beyond 8 weeks, relapsed more than
once after improvement or resolution of symp-
toms, or required maintenance therapy with more
than one additional course of intravenous
immunoglobulin (IVIg) or plasma exchange, and/
or immunosuppressants.
Electrodiagnostic records, including nerve con-
duction study waveforms (when available) and data
sheets, were reviewed for all study patients. Motor
and sensory conduction studies were performed
using standard techniques. Only the first studies
performed within 4 weeks of onset were used for
analysis. Patients whose initial electrophysiological
studies were done at >4 weeks after onset were
excluded. All electrophysiological studies were per-
formed at the London Health Sciences Centre,
with the exception of 5 patients whose first studies
were performed at another center before transfer.
These patients all had repeat studies at least once
at our center to ensure agreement with the electro-
diagnostic conclusions, but the data from the first
studies were used for analysis.
The Inflammatory Neuropathy Cause and Treat-
ment Group (INCAT) electrodiagnostic criteria were
used for the definitions of conduction block, temporal
dispersion, reduced conduction velocity, prolonged
latency, and abnormal F-waves to ensure that all the
patients had a demyelinating polyneuropathy.17
Several definitions of a sural-sparing pattern
can be found in the literature.7–13 All the different
possibilities were considered, including:
1. Abnormal median SNAP amplitude (low or
absent) with a normal sural SNAP amplitude.10
2. Absent median SNAP with a normal sural SNAP
amplitude.11
3. Normal or relatively preserved sural SNAP com-
pared with at least two abnormal upper extrem-
ity SNAPs (median, ulnar, radial).8
4. Abnormal median or ulnar SNAP (low or absent
response) with a normal sural SNAP amplitude.7
The sensory ratio was calculated as follows:
(sural þ radial)/(ulnar þ median) SNAP
2 AIDP vs. A-CIDP MUSCLE & NERVE Month 2009