SLR - December 2019 - Howard C. Chang
Reference: Lee A, Kwon HK. Early Detection of Diabetic Polyneuropathy Using Paired Stimulation Studies of the Sensory Nerves. Am J Phys Med Rehabil. 2019;98(11):982-988.Scientific Literature Review
Reviewed By: Howard C. Chang, DPM
Residency Program: Regions Hospital/HealthPartners Institute – St. Paul, MN
Podiatric Relevance: Approximately 30-50 percent of diabetic patients are affected by polyneuropathy, with as many as half without complaints of any symptoms. Diabetic polyneuropathy (DPN) is often complicated by neuropathic ulceration, which puts the patient at an increased risk for infection and subsequent amputation. Electrodiagnostic studies (EDS) such as a nerve conduction study (NCS) are commonly employed for detection of DPN; the aim of the study is to evaluate a component of the NCS, the relative refractory period (RRP), as an early indicator of DPN.
Methods: The authors performed a prospective study comparing 88 patients with known diabetes to 26 healthy controls from one institution from September 2017 to September 2018. Exclusion criteria included: chronic alcohol intake (>14g pure EtOH/daily) or chronic kidney disease (CKD) (GFR <60ml/min per 1.73 m2.) Additionally, patients with confirmed carpal tunnel syndrome on electrodiagnostic studies were also excluded from the analysis. Nerve conduction studies and needle electromyography were performed using a paired stimulus method in unilateral upper and lower limbs. Sensory nerve action potentials (SNAPs) were recorded. Peak latencies and amplitudes were measured. Relative refractory period was defined as the shortest interstimulus interval at which the latency of the SNAP to the second stimulus becomes equal to that of the first.
Results: Patients were grouped into DPN (+) and DPN (-) based on criteria set out by the Diabetes Control and Complication Trial for EDS. Thirty-one diabetic patients and three healthy controls met criteria for carpal tunnel syndrome and were excluded from the analysis. Of the 57 remaining diabetics, 31 met criteria for DPN and 26 did not. The RRP of the median and sural nerves were significantly more delayed in the diabetic patients (3.6 msec, p = <0.001 and 3.8 msec, p <0.001 respectively) compared to control (3.0 msec for both nerves). Of the diabetics that did not meet DPN criteria (n = 26) and diabetics who were clinically asymptomatic (n = 29), the RRP was still prolonged for both median (3.3 msec, p-value=0.002) and sural nerves (3.5 msec, p <0.001) compared to control. RRP sensitivity and specificity for DPN was 85.7 percent and 65.5 percent for the median nerve and 80.8 percent and 72.4 percent for the sural nerve. When using EDS as a whole to diagnose DPN, the sensitivity and specificity was 82.1 percent and 72.4 percent respectively.
Conclusions: RRP is altered in demyelinating neuropathies as well as axonopathies. Prolongation of the refractory period is an early manifestation of changes in the excitability of a nerve, a first sign of neuropathy. RRP has comparable sensitivity to the conventional criteria for DPN with electrodiagnostic studies, but is much simpler apply. This allows for a more efficient means of detecting early polyneuropathy in diabetic patients.