Abstract
Sural sparing defined as absent/abnormal median sensory nerve action potential (SNAP) amplitude or absent/abnormal ulnar SNAP amplitude with a normal sural SNAP amplitude is thought to be a marker for inflammatory demyelinating polyneuropathies. If sural sparing pattern specifically defined as absent/abnormal median and ulnar SNAP amplitude with normal sural SNAP amplitude (AMUNS) is sensitive and specific when compared with either absent/abnormal median and normal sural (AMNS) or absent/abnormal ulnar and normal sural (AUNS) for acute inflammatory demyelinating polyneuropathy (AIDP), chronic inflammatory demyelinating polyneuropathy (CIDP), select non-diabetic axonopathies (AXPs), and diabetic neuropathies (DNs). Retrospective analysis from 2001 to 2010 on all newly diagnosed AIDP, CIDP, select non-diabetic AXP, and DN. There were 20 AIDP and 23 CIDP. Twenty AXP and 50 DN patients between 2009 and 2010 were included as controls. AMUNS was seen in 65% of AIDP, 39% CIDP compared with 10% of AXP and 6% for DN with sensitivity of 51%, specificity of 92%, whereas the specificity of AMNS/AUNS was 73% and its sensitivity was 58%. If a patient has AMUNS they are >12 times more likely to have AIDP (p < 0.001). Sural sparing is highly specific but not sensitive when compared with either AMNS or AUNS in AIDP but does not add to sensitivity or specificity in CIDP.
Highlights
A common scenario where nerve conduction studies are of particular use is in differentiating primary axonal from primary demyelinating neuropathies (DMNs).Sensory electrodiagnostic studies routinely performed are rarely, if at all used in this setting
A total of 50 acute inflammatory demyelinating polyneuropathy (AIDP) and 82 chronic inflammatory demyelinating polyneuropathy (CIDP) cases were reviewed over the period of 2001–2010
AIDP cases not included were due to the lack of EDX studies or incomplete EDX data prior to treatment
Summary
A common scenario where nerve conduction studies are of particular use is in differentiating primary axonal from primary demyelinating neuropathies (DMNs).Sensory electrodiagnostic studies routinely performed are rarely, if at all used in this setting. Sural sparing defined variously as normal or relatively preserved sural sensory nerve action potential (SNAP) amplitude with abnormal/absent median SNAP amplitude and/or abnormal/ absent ulnar SNAP amplitude and/or abnormal/absent radial SNAP amplitude [7,8,9,10,11] has been known to be a highly specific marker for DMNs. Previous studies that looked into sensitivity and specificity of sural sparing pattern in either AIDP [7, 8] or CIDP [10, 11] lacked a uniform definition for sural sparing and in many cases patients were already on treatment potentially confounding the EDX results. Sural sparing defined as absent/abnormal median sensory nerve action potential (SNAP) amplitude or absent/abnormal ulnar SNAP amplitude with a normal sural SNAP amplitude is thought to be a marker for inflammatory demyelinating polyneuropathies
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