Terminal latency index in polyneuropathy with IgM paraproteinemia and anti‐MAG antibody

Abstract

Criteria for the diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) are met by the polyneuropathy associated with immunoglobulin M (IgM) paraproteinemia and anti-myelin-associated glycoprotein (MAG) antibody (MAG-CIDP). However, MAG-CIDP differs from other types of CIDP, mainly in its poorer response to treatment. The utility of terminal latency index (TLI) as an electrophysiological marker for MAG-CIDP has been debated. In this study we confirmed its diagnostic usefulness and evaluated TLI threshold values for motor nerves investigated in routine nerve conduction studies. Median, ulnar, peroneal, and tibial TLIs of 11 subjects with MAG-CIDP, 18 with CIDP, and 76 healthy controls were compared, and threshold values for MAG-CIDP evaluated as the lowest value with a likelihood ratio higher than 10. Mean TLI values and TLIs of all but the peroneal nerve were significantly lower in MAG-CIDP. Median nerve TLI of 0.26 and ulnar nerve TLI of 0.33 were identified as the threshold TLI values for MAG-CIDP.

Terminal latency index in neuropathy with antibodies against myelin‐associated glycoproteins

“…2,5,6,11,19 Median TLI alone was sufficient to distinguish between MAG/SGPG-N and HMSN1 with a high specificity and moderately high sensitivity. Patients with median nerve TLI Ͻ0.26 had MAG/SGPG-N and those with TLI Ͼ0.32 had HMSN1.…”

“…2,5,6,29 A direct comparison of our data with those TLI values is difficult since it is influenced by the distal distance, which varied in different studies. Ulnar TLI was additionally evaluated in one study to increase the specificity in distinguishing MAG/SGPG-N from CIDP, 2,6 but in our study the combination of median and ulnar TLI did not appreciably improve classification into MAG/ SGPG-N or HMSN1.…”

“…2,5,29 TLI was shown to be significantly lower in patients with anti-MAG neuropathy than in those with CIDP. 6 In the upper extremity, TLI allows comparative assessment of the conduction time along the distal (wrist-to-thenar) nerve segment with that of the intermediate segment (elbow-to-wrist). MFR compares the conduction time along the distal segment of a nerve with its proximal one (spinal cord-to-elbow).…”

POEMS Syndrome Presenting with Acute Demyelinating Polyneuropathy: Increased Terminal Latency Indices and Uniform Demyelination

“…In our patient, the TLIs of both peroneal nerves (0.62 and 0.60), both tibial nerves (0.63 and 0.58) and the right ulnar nerve (0.47) were greater than the mean values, as previously reported, although those of both median nerves (0.28 and 0.29) and the left ulnar nerve (0.38) were not greater than previously reported values. Cocito et al (12) measured TLIs in typical CIDP patients, as follows: 0.34-0.40 (median), 0.41-0.47 (ulnar), 0.34-0.38 (peroneal) and 0.40-0.48 (tibial). Compared to the values observed in these CIDP patients, the TLIs of our patient were also much higher in the lower extremities.…”

Chronic inflammatory demyelinating polyneuropathy

“…Die therapeutisch zu erzielende Verbesserung scheint aber bei Diabetes-Patienten geringer zu sein als bei CIDP-Patienten ohne Diabetes [24,13], was möglicherweise die vorbestehende Schädigung aufgrund einer latenten oder manifesten diabetischen Neuropathie widerspiegelt. [14] schlagen vor, dass die distale motorische Latenz, berechnet als "terminal latency index TLI" (distale Leitungsdistanz [mm]/Nervenleitgeschwindigkeit [m/s]×distal motorische Latenz [ms]), sensitiv die CIDP bei IgM-Paraproteinämie von anderen Formen des CIDP differenziert. Der reduzierte TLI ist auch zusammen mit einer verminderten sensiblen Nervenleitgeschwindigkeit bei normaler oder gering reduzierter motorischer Nervenleitgeschwindigkeit differenzialdiagnostisch hinweisend auf eine hereditäre Neuropathie mit Neigung zu Druckläsionen (HNPP, [3]).…”