Sensory sparing patterns and the sensory ratio in acute inflammatory demyelinating polyneuropathy

Abstract

The relative preservation (sparing) of sural sensory nerve action potentials (SNAPs) is a useful diagnostic finding in patients with acute inflammatory demyelinating polyneuropathy (AIDP). However, recording of sural SNAPs is not always technically feasible, especially in obese, edematous, or elderly individuals. Hence, we systematically evaluated the predictive values of the commonly employed SNAPs in the diagnosis of AIDP within 2 weeks from onset of symptoms. Sensory sparing patterns and sensory ratios of the sural, radial, median, and ulnar SNAPs of AIDP patients were included in a retrospective and blinded analysis, and compared to patients with diabetic polyneuropathy (DPN) and controls. Logistic regression models for the sural plus radial SNAPs/median plus ulnar SNAPs (sensory ratio) were constructed. A sural sparing pattern was present only in the AIDP group (34.4%, P < 0.001). A radial sparing pattern did not discriminate the AIDP from the DPN groups. The sural/radial sensory ratio was useful to ascertain DPN, but did not discriminate AIDP from controls. The sensory ratio was higher in AIDP compared to DPN and controls and was an independent predictor for AIDP. This study implies that the sensory ratio is a useful predictor for the diagnosis of AIDP and may substitute for sural sparing in technically difficult situations.

Sensory Conduction Study in Fisher Syndrome: Patterns of Abnormalities and Their Clinical Correlation

“…the median or the ulnar nerve). A sural-sparing pattern was defined as normal sural responses compared to abnormal upper limb sensory responses, or relatively preserved sural response compared to at least one absent sensory response in the upper limb [8,9,10]. A median neuropathy across the wrist was defined as median sensory CV across the wrist of <43 m/s [16].…”

“…Demyelination is difficult to demonstrate in sensory conduction studies. However, a sural-sparing pattern, also known as a normal sural-abnormal median pattern, is useful for the diagnosis of a primary demyelinating neuropathy [7,8,9]. This pattern of sensory conduction abnormality was also one early electrodiagnostic finding in GBS [10,11].…”

The Application of Clinical, Electrophysiological and Nerve Ultrasound Parameters in Distinguishing Acute-onset Chronic from Acute Inflammatory Demyelinating Polyneuropathy

“…24 The sensory ratio can be calculated as (sural + radial) ÷ (ulnar + median) sNAP amplitudes. 25 According to literature reports, the later electrophysiological parameters do not seem to be statistically different between the acute-onset CIDP and the AIDP patients. [16][17][18] Although the sural-sparing pattern or the elevated sensory ratio might be useful to differentiate an acquired demyelinating polyneuropathy from a length-dependent axonal polyneuropathy, recent studies show that these patterns occur equally in both AIDP and CIDP.…”

“…[16][17][18] Although the sural-sparing pattern or the elevated sensory ratio might be useful to differentiate an acquired demyelinating polyneuropathy from a length-dependent axonal polyneuropathy, recent studies show that these patterns occur equally in both AIDP and CIDP. 16,[23][24][25] On the other hand, the A-wave is attributed to either sprouting phenomena or ephaptic/ectopic discharges. In the case of CIDP, it could be a sign of functional recovery, whereas in AIDP, it could be an early indicator of demyelination.…”

Guillain-Barré Syndrome and Related Disorders

“…Among them, a sensory ratio (sural + radial SNAPs/median + ulnar SNAPs) is a good substitute for sural-sparing pattern. Patients with AIDP are 12 times more likely to have an elevated sensory ratio (>1) compared to patients with axonal polyneuropathies such as diabetic or critical illness polyneuropathies [ 115 ] . It is not known whether another lower limb SNAP, such as the super fi cial peroneal, could substitute for the sural.…”