Shinshu Med J, 72⑵：87～94, 2024

Analysis of Distal Compound Muscle Action Potential Durationin Hereditary Transthyretin Amyloidosis with Polyneuropathy
Yumi Hoshino1）, Minori Kodaira1）＊, Nobuhiko Ohashi1）
Hiroshi Morita2） and Yoshiki Sekijima1）3）
1） Department of Medicine (Neurology and Rheumatology), Shinshu University School of Medicine
2） Center for Health, Safety and Environmental Management, Shinshu University
3） Institute for Biomedical Sciences, Shinshu University

Background : Hereditary transthyretin (ATTRv) amyloidosis, a disorder accompanied by axonal polyneuropathy,
is often misdiagnosed as chronic inflammatory demyelinating polyneuropathy (CIDP). Prolongation of distally
evoked compound muscle action potential duration (DCMAPD), an electrophysiological parameter of heterogeneous
conduction delay at the distal part of the motor nerve suggesting demyelinating neuropathies, is included in an
index of diagnostic criteria for CIDP. However, DCMAPDs are strongly influenced by low-frequency filtering(LFF) settings, which differ across hospitals worldwide.
Aim : To analyze DCMAPD in patients with ATTRv amyloidosis with polyneuropathy (ATTRv-PN).
Methods : DCMAPs of the median, ulnar, tibial, and peroneal nerves were recorded under LFF settings of 2, 10,
and 20 Hz in 50 patients with ATTRv-PN. The changes of DCMAPD accompanied with the changes of LFF
settings were analyzed. The appropriateness of the cut-off values of the DCMAPD in the latest criteria for CIDP,
which defined under various LFF settings, was also validated in ATTRv-PN patients.
Results : The DCMAPD was shorter with increasing LFF settings. Less than 10 ％ of patients with ATTRv-PN
demonstrated prolonged DCMAPD of the ulnar, tibial, and peroneal nerves. In contrast, ten patients demonstrated
prolonged DCMAPD in the median nerve under LFF settings of 2, 10, and/or 20 Hz. Nine of the ten cases werecomplicated with carpal tunnel syndrome (CTS).
Conclusion : Prolongation of DCMAPDs in the ulnar, tibial, and peroneal nerves is rare in ATTRv-PN patients.
DCMAPD analysis of the median nerve in patients with ATTRv-PN requires caution, because they frequently
develop CTS and those with CTS may demonstrate prolonged DCMAPD. Shinshu Med J 72 : 87―94, 2024
(Received for publication October 6, 2023 ; accepted in revised form December 20, 2023)
Key words : ATTRv amyloidosis, CIDP, low-frequency filtering, CMAP duration, carpal tunnel syndrome
Ⅰ Introduction

gressive axonal polyneuropathy2）. Liver transplanta­tion had been the only life-saving treatment. However,Hereditary transthyretin (ATTRv) amyloidosis is a

TTR tetramer stabilizers and nucleic acid therapeutics

life-threatening and gain-of-toxic-function disease char­

have been developed and have shown greater treatment

acterized by the extracellular deposition of amyloid

effects3）-6）. In these situations, early diagnosis andfibrils composed of the transthyretin (TTR)1）. Most

treatment initiation are becoming more important.

patients with ATTRv amyloidosis demonstrate pro­However, early diagnosis of ATTRv amyloidosis may
be difficult. Notably, several patients with ATTRv＊

Corresponding author : Minori Kodaira
Department of Medicine (Neurology and Rheumatology)
Shinshu University School of Medicine, 3-1-1 Asahi,
Matsumoto, Nagano 390-8621, Japan
E-mail : mkodaira@shinshu-u.ac.jp

No. 2, 2024

amyloidosis with polyneuropathy (ATTRv-PN) from
non-endemic areas without a family history are mis­diagnosed with other neuropathies, especially chronic
inflammatory demyelinating polyneuropathy (CIDP)7）8）.
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Hoshino・Kodaira・Ohashi et al.

A nerve conduction study (NCS) is a useful electrophysi­

The clinical stage of patients with ATTRv amyloido­

ological tool for identifying the underlying pathophys­

sis was defined using the criteria of Countinho et al.

iology in patients with neuropathy. However, patientscriteria16）: Stage 0 : patients have some autonomic dys­

with ATTRv-PN occasionally exhibit conduction de­function without polyneuropathic symptoms or signs ;lay, fulfilling the electrodiagnostic criteria of CIDP

Stage I : polyneuropathy is localized to the lower

without a conduction block under severe axonal de­limbs, and patients can walk without assistance ;9）10）

generation

Stage II : polyneuropathy involving the upper and.

Prolongation of distally evoked compound muscle

lower limbs, and patients are disabled but can stillaction potential duration (DCMAPD), an electrophys­

walk with assistance ; Stage III : severe polyneuropa­

iological parameter of heterogeneous conduction delay

thy and autonomic dysfunction confining patients toat the distal part of the motor nerve suggesting de­a wheelchair or bed.

myelinating neuropathies, is included in an index of

Ｂ

11）
-13）

criteria for CIDP

Electrophysiological examinations. The cut-off value of DCMAPD

All NCSs were performed using a MEB2312 (Nihon-in the European Federation of Neurological Societies/

Koden, Tokyo, Japan). Motor NCSs were performed

Peripheral Nerve Society (EFNS/PNS) 2010 diagnostic

using the belly-tendon method on the one-sided me­

criteria for CIDP had been based on results obtained

dian, ulnar, tibial, and peroneal nerves17）. The dis­

under only a low-frequency filtering (LFF) of 20 Hz11）12）.

tance from the cathode of the recording electrode to

However, the DCMAPD recorded under lower LFF

the stimulating electrode cathode for measuring distal

14）
15）

. Furthermore, LFF

latency was 7, 7, 10, and 8.5 cm for the median, ulnar,

settings differ across hospitals worldwide. Accordingly,

tibial, and peroneal nerves, respectively. CMAP am­

Mitsuma et al. proposed cut-off values of DCMAPD

plitude, distal latency (DL), motor nerve conduction

under LFF settings of 2, 5, 10, and 20 Hz to diagnose

velocity (MCV), F-wave latency, and DCMAPD weresettings is more prolonged

15）

CIDP . They defined these cut-off values based on

measured in motor NCSs. CMAP amplitude was de­

the results of NCSs in patients with typical CIDP and

fined as the amplitude between the baseline and neg­diabetic polyneuropathy, and healthy subjects. Recently,

ative peak. DCMAPD was defined as the period fromthese cut-off values proposed by Mitsuma et al. havethe onset of the initial negative phase to the return

been recommended for the analysis of DCMAPD by

to the baseline of the last negative deflection of thethe latest CIDP criteria, the revised European Academy

CMAP at a sensitivity of 500 μV/div. High-frequencyof Neurology/Peripheral Nerve Society (EAN/PNS)

filtering (HFF) was set and fixed at 10 kHz throughout

13）
15）

. Validation of these cut-the motor NCSs. LFF was set at 2 Hz. The LFF set­off values under each LFF setting in diseases occa­ting was changed from 2 Hz to 10 Hz and 20 Hz only

sionally misdiagnosed as CIDP is needed. We analyzed

when the DCMAPDs were recorded to evaluate the2021 guideline for CIDP

the effects of LFF settings on DCMAPD and validated

effects of the LFF settings on the DCMAPD. A hum

whether the cut-off values of DCMAPD under each LFF

filter was not used. Sensory NCSs were conductedsetting are appropriate in patients with ATTRv-PN.

on the median, ulnar, and sural nerves using an anti­

Ⅱ Methods
Ａ

Participants

dromic method17）. In the median and ulnar nerves,the cathode of the stimulating electrode was placedon the wrist in the same position as the motor NCSs

Patients with disease-causing variants of TTR

of each nerve. In the sural nerve, the stimulating

genes and TTR-derived amyloid deposition in biopsy

electrode cathode was placed 14 cm proximal to thespecimens were included in this study. All patientscathode of the recording electrode. Amplitude of sen­showed symptoms of polyneuropathy, and those withsory nerve action potential (SNAP) and sensory nerve

other factors affecting peripheral nerve function, suchconduction velocity (SCV) were measured in senso­

as diabetes mellitus and alcoholism, were excluded.

ry NCSs. The SNAP amplitude was defined as the88

Shinshu Med J

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CMAP duration in ATTRv

amplitude between the initial positive and negative
peaks. The HFF and LFF were fixed at 3 kHz and
20 Hz, respectively, during sensory NCSs. The skintemperature of the examined segment was ≥ 30 ℃
throughout the electrophysiological examination.
Ｃ

Analyses
The effects of LFF settings on DCMAPD were

evaluated using the Jonckheere-Terpstra test, whichis consistent with previous studies15）. The DCMAPD
was analyzed according to the EAN/PNS 2021 crite­
ria for CIDP. Correlations between the DCMAPD re­corded under an LFF setting of 2 Hz and other electro­
physiological parameters, including CMAP amplitude,
DL, MCV, F-wave latency, SNAP, and SCV, correspond­
ing to each nerve, were analyzed using Spearman’srank correlation coefficient. Correlations between

Table 1Age (y)Female/MaleAge at onset of neuropathy (y)Duration from onset of neuropathy (y)Duration from start of treatments (y)Presence of family history (％)
Patients from non-endemic area (％)
Clinical Stage Ⅰ (％)
Clinical Stage Ⅱ (％)
Clinical Stage Ⅲ (％)
Complication of carpal tunnel syndrome

NCS in the sural nerve. When a group with abnormallyprolonged DCMAPD was detected, subgroup analyses
between patients with and without prolonged DCMAPD
were performed using the Mann-Whitney U test or
Fisher’s exact test. Statistical significance was set at
p＜0.05. Statistical analysis was performed using the

52.4±14.5
16/34
42.8±15.3
10.4±6.3
6.7±5.8
86
64
42
52
6
17

Data are presented as mean ± SD. y : years
Treatments include liver transplantation, transthyretin
tetramer stabilizers, or oligonucleotide therapeutics.
Table 2 The DCMAPDs of the median, ulnar, tibial, andperoneal nerves under each LFF setting

DCMAPD in the lower limb nerves and sensory nerve
function were analyzed using the results of the sensory

Patients’ clinical background

2 Hz
Median (ms)
Ulnar
(ms)
Tibial(ms)
Peroneal (ms)

6.9 (1.5)
6.8 (1.2)
6.1 (1.9)
6.9 (1.7)

LFF settings
10 Hz
20 Hz
6.4 (1.4)
6.6 (1.3)
5.8 (1.3)
6.6 (1.6)

5.8 (1.2)
6.0 (1.1)
5.6 (1.4)
6.3 (1.8)

Data are presented as mean (SD).
DCMAPD, distally evoked compound muscle action po­
tential duration ; LFF, low-frequency filtering.

Bell Curve for Excel (Social Survey Research Infor­

two Ser50Ile (Ser70Ile), two Phe44Ser (p. Phe64Ser), one

mation Co., Ltd., Japan).

Ser50Arg (p. Ser70Arg), one Ser90Arg (p. Ser110Arg),Ｄ

one Thr60Ala (p. Thr80Ala), one Ala36Pro (p. Ala56Pro),

Protocol approval and ethical concerns
The Shinshu University Certified Review Board of

one Glu42Gly (p. Glu62Gly), one Tyr114His (p. Tyr134His),

Clinical Research approved this prospective study

and one Phe53Val (p. Phe73Val)]. Forty-five patients(approval number : 4244) and written informed consent

received disease-modifying therapies, such as liver

was obtained from each patient.

transplantation, TTR tetramer stabilizers (tafamidis),

Ⅲ Results
Ａ

Background of patients with ATTRv-PN
Fifty patients with ATTRv-PN were included inthis study. The clinical profiles of patients are shown

and/or ribonucleic acid interference therapy (patisiran).
The clinical stage of most patients was either stage I
or II. Seventeen cases were complicated with carpal
tunnel syndrome (CTS).
Ｂ Effects of LFF settings on DCMAPD in ATTRv-

in Table 1. Notably, 86 ％ of the patients had a family

PN patients

history of ATTRv amyloidosis, and 36 ％ were from

CMAPs were not detected in the median, ulnar,

an endemic area of ATTRv in Nagano Prefecture. Six

tibial, and peroneal nerves in three, one, 11, and 16

patients from non-endemic areas had no apparent

patients, respectively. Therefore, the effects of LFF

family history of ATTRv amyloidosis. Thirty-fivesettings on the DCMAPD of the median, ulnar, tibial,

patients had the TTR variant, Val30Met (p.Val50Met).

and peroneal nerves were analyzed in 47, 49, 39, andFifteen patients had non-Val30Met variants [two34 patients, respectively. The effects of the LFF set­Ile107Val (p. Ile127Val), two Asp38Ala (p. Asp58Ala),tings on the DCMAPD are summarized in Table 2.

No. 2, 2024

89

Hoshino・Kodaira・Ohashi et al.
Table 3Results of electrophysiological examinations.

Nerve

CMAP (mV)

DL (ms)MCV (m/s)

F-wave latency (ms)

SNAP (μV)

SCV (m/s)

MedianUlnar
TibialPeroneal
Sural

7.3 (4.8)
6.4 (3.9)
6.1 (6.3)
1.5 (1.7)

4.1 (1.2)
3.1 (0.9)
4.1 (0.9)
4.5 (0.9)

50.8 (8.8)
55.7 (9.9)
44.4 (7.1)
43.0 (5.9)

29.1 (5.1)
28.9 (5.3)
49.2 (5.8)
50.7 (4.1)

10.8 (11.2)
10.2 (10.5)

53.7 (10.3)
51.5 (9.6)

5.3 (6.5)

48.1 (5.6)

Data are presented as mean (SD).
CMAP, compound muscle action potential ; DL, distal latency ; MCV, motor nerve conduction velocity ; SCV, sensory
nerve conduction velocity ; SNAP, sensory nerve action potential
Table 4 The proportion of patients showing prolonged DCMAPD according to the EAN/PNS 2021 criteria
Nerve

Number of patientsMedianMedianUlnar
TibialPeroneal

31 without CTS
17 with CTS
49
39
34

Number of patients showing prolongation of DCMAPD
2 Hz

10 Hz

20 Hz

0 (0 ％)
8 (47.1 ％)
2 (4.1 ％)
1 (2.6 ％)3 (8.8 ％)

1 (3.0 ％)
7 (41.2 ％)
2 (4.1 ％)
1 (2.6 ％)
4 (11.8 ％)0 (0 ％)
6 (35.3 ％)2 (4.1 ％)
1 (2.6 ％)3 (8.8 ％)＜Cut-off value of DCMAPD13＞Median ＞ 8.4 ms, Ulnar ＞ 9.6 ms, Tibial ＞ 9.2 ms, and Peroneal ＞ 8.8 ms under an LFF setting of 2 Hz.
Median ＞ 7.8 ms, Ulnar ＞ 8.5 ms, Tibial ＞ 8.2 ms, and Peroneal ＞ 8.3 ms under an LFF setting of 10 Hz.
Median ＞ 7.4 ms, Ulnar ＞ 7.8 ms, tibial ＞ 8.0 ms, and Peroneal ＞ 8.1 ms under an LFF setting of 20 Hz.
CTS, carpal tunnel syndrome ; DCMAPD, distally evoked compound muscle action potential duration ; LFF, lowfrequency filtering.

As the LFF setting increased, the DCMAPD of the

10 ％ of patients, except for those with DCMAPD of

median, ulnar, and peroneal nerves became shorter

the peroneal nerve under the LFF setting of 10 Hz)(p＜0.001, p＜0.001, p＜0.05, respectively). The effectshowed prolonged DCMAPD of the ulnar, tibial, andof LFF on the DCMAPD of the tibial nerve was in­peroneal nerves, fulfilling the EAN/PNS 2021 criteria

significant (p＝0.08). However, DCMAPD tended to(Table 4). On the other hand, 10 patients showed pro­be shorter under higher LFF settings.

longed DCMAPD of the median nerve under LFF set­Ｃ Relationship between DCMAPD and other elec-tings of 2 Hz, 10 Hz, and/or 20 Hz. The clinical stages

trophysiological parameters

were Ⅰ and Ⅱ in two and eight patients, respectively.

The results of the other electrophysiological exam­

The ten patients with prolonged DCMAPD of theinations are summarized in Table 3. The SCV was nega­

median nerve had slower MCV (p＜0.01) and SCV (ptively correlated with DCMAPD in the median nerve＜0.05) in the median nerve than those without pro­

(rs＝－0.35, p＜0.05). MCV was also negatively cor­longed DCMAPD of the median nerve. They also

related with DCMAPD in the ulnar nerve (rs＝－0.32,

tended to show a longer DL (p＝0.07) and smaller

p＜0.05). No other parameters correlated with DCMAPD

SNAP (p＝0.09) in the median nerve than the latter.

in any of the nerves.

Patients with prolonged DCMAPD of the medianＤ Prolonged DCMAPD in ATTRv-PN using CIDP

nerve also tended to have longer DCMAPD of theelectrodiagnostic criteria

ulnar nerve under an LFF setting of 2 Hz (p<0.05)

Table 4 shows the number of patients with pro­and DCMAPD of the peroneal nerve under LFF set­longed DCMAPD, according to the EAN/PNS 2021

tings of 2, 10, and 20 Hz (p＜0.05, p＜0.005, p＜0.05,

diagnostic criteria for CIDP. Only a few patients (＜respectively). However, other electrophysiological

90

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CMAP duration in ATTRv

Fig. 1 Changes of DCMAPD in the median nerve follow­
ing stimulation at the wrist under LFF settings of
2, 10, 20Hz(a) CMAPs without prolongation of DCMAPD in patientswith ATTRv-PN without CTS. (b) CMAPs with prolon­
gation of DCMAPD in patients with ATTRv-PN with CTS.
ATTRv-PN, hereditary transthyretin amyloidosis withpolyneuropathy ; CMAP, compound muscle action poten­
tial ; CTS, carpal tunnel syndrome ; DCMAPD, distally
evoked compound muscle action potential duration ; LFF,
low-frequency filtering.

parameters of the ulnar, tibial, peroneal, and suralin patients with ATTRv-PN became shorter as thenerves did not differ between patients with and

LFF setting increased. DCMAPD was determined towithout prolonged DCMAPD of the median nerve. Of

be within normal limits in most patients with ATTRv-

the 10 patients with prolonged DCMAPD of the me­

PN according to the EAN/PNS 2021 criteria, whichdian nerve, two had a surgical history of CTS and

defines the cut-off values of DCMAPD under eachseven showed compatible clinical symptoms and

LFF setting. However, more than one third of ATTRv-

signs of CTS. In contrast, eight of the remaining 37

PN patients with CTS show prolonged DCMAPD ofpatients without prolonged DCMAPD had a surgicalthe median nerve, even when the cut-off values ofhistory of CTS (n＝3) or clinical symptoms and signs

the EAN/PNS 2021 criteria were used.

of CTS (n＝5). Compared to ATTRv-PN patientsＡ Effects of LFF on DCMAPD in ATTRv-PN

without CTS, those with CTS tended to develop pro­patients

longed median nerve DCMAPD (p＜0.001). Fig. 1.

The effects of LFF settings on DCMAPD in patientsshows representative CMAP waveforms and changes

with ATTRv-PN were consistent with the results ofof DCAMPD according to LFF settings in the medianprevious studies in healthy participants and patients

nerve from ATTRv-PN patients without and with

with diabetic neuropathy or CIDP14）15）. DCMAPDs of

CTS.

the median, ulnar, and peroneal nerves became shorter
Ⅳ Discussion

as the LFF setting increased. A similar tendency wasobserved in the tibial nerve. The effects of the LFF

This study confirmed the significant effects of LFF

setting on tibial nerve DCMAPD were not statisticallyon DCMAPD in patients with ATTRv-PN. DCMAPD

significant, which may be due to the difficulty in pre­No. 2, 2024

91

Hoshino・Kodaira・Ohashi et al.

cisely measuring DCMAPD in small CMAPs because

tients with CTS tended to show prolonged DCMAPD

of contamination from potential spreads of otherof the median nerve, even when analyzed using themuscles18）

and electrical stimulating shock artifacts

cut-off values of the EAN/PNS 2021 criteria. Patients

following high-intensity electrical stimulation to de­with prolonged DCMAPD of the median nerve also

tect CMAPs under severe axonal degeneration.

tended to have longer DCMAPD of the ulnar and

DCMAPD did not correlate with other electrophys­

peroneal nerves ; however, other parameters of neu­

iological parameters of each nerve ; however, a weakrophysiological examinations, except for those of thenegative correlation was observed between DCMAPD

median nerve, did not show any differences between

and SCV in the median nerve and between DCMAPD

patients with and without prolongation of DCMAPD

and MCV in the ulnar nerve. These results show

in the median nerve. Furthermore, most of ATTRv-

that DCMAPD in patients with ATTRv-PN is less

PN patients did not develop prolongation of DCMAPD

involved in the severity of damage in each nerve ;in the ulnar, tibial, and peroneal nerves. These results

however, it is strongly affected by the LFF settings.

also suggest that CTS may have a big influence on

Ｂ Analysis of DCMAPD in ATTRv-PN using theprolongation of DCMAPD in the median nerve of pa­

latest criteria for CIDP

tients with ATTRv-PN. Mitsuma et al. reported that

Patients with ATTRv-PN ideally should not showless than 5 ％ of patients with diabetic polyneuropathy

prolongation of DCMAPD, because primary patho­

without CTS showed prolongation of DCMAPD sur­

physiology of them is axonal damage. In our retro­passing the cut-off values of the revised EAN/PNS

spective study using NCSs in the ulnar and tibial

2021 criteria15）. At present, the effects of CTS with or

nerves9）, we observed that 45 ％ of the patients withwithout axonal polyneuropathy on DCMAPD have

ATTRv-PN demonstrated prolonged DCMAPD in the

not been established. Although pathological analysis

ulnar nerve recorded under an LFF setting of 2 Hzof CTS in humans is scarce19）, focal demyelination andcompared with the cut-off value of DCMAPD ( ≥ 6.7

remyelination have been observed in a rat model of

ms in the ulnar nerve) of the EFNS/PNS 2010 diag­CTS using chronic nerve compression to the sciatic

nostic criteria for CIDP based on results of DCMAPD

nerve20）. In the experimental study using rats, het­

obtained under a LFF setting of 20Hz. Contrarily, weerogeneous demyelination and remyelination (i.e., re­confirmed that only 2 ％ of the patients with ATTRv

gion was located at the outer half of the nerve withshowed prolongation of DCMAPD in the ulnar nerve,

normal finding at the center half) was also observed

fulfilling the cut-off value (＞9.6 ms) under the LFF

at early stage of chronic compression20）. Investigation

setting of 2 Hz proposed by Mitsuma et al.15） in theof DCMAPD in patients with CTS alone using thestudy. However, the effects of LFF settings, except

cut-off values of the revised EAN/PNS 2021 criteria isfor 2 Hz, on DCMAPDs in the ulnar and tibial nerves

needed ; however, results of these pathological studies

and DCMAPDs in the median and peroneal nerves

support a notion that CTS may induce prolongation ofhave not been investigated in patients with ATTRv-

DCMAPD in the median nerve. Analysis of DCMAPD

PN.

in the median nerve of patients with ATTRv-PN re­

The results of DCMAPD in the ulnar, peroneal, andtibial nerves in the present study confirmed that thequires caution, because they frequently develop CTS21）.
Ｃ

Limitations

use of the cut-off values of DCMAPD under each LFF

Of the study participants, 36 ％ of the patients weresetting indicated in the revised EAN/PNS 2021 crite­from an endemic area for ATTRv amyloidosis, andria for CIDP minimizes the misinterpretation of pro­they all had a family history of ATTRv amyloidosis.

longed DCMAPD in patients with ATTRv-PN. Simi­

Furthermore, 86 ％ of participants, including patients

larly, DCMAPD of the median nerve in ATTRv-PN

from non-endemic areas, had family history of ATTRv

without CTS did not prolong.

amyloidosis. These patients are less likely to be mis­

In contrast, this study found that ATTRv-PN pa­
92

diagnosed as having CIDP in clinical practice.
Shinshu Med J

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CMAP duration in ATTRv

suggestive of demyelinating neuropathies.

Ⅴ Conclusion

Conflict of interest

Prolongation of DCMAPDs in the ulnar, tibial, andperoneal nerves is rare in patients with ATTRv-PN
by using the cut-off values of DCMAPD under each

The authors declare that they have no conflicts ofinterest.

LFF setting. Analysis of DCMAPD of the medianFunding

nerve in patients with ATTRv-PN requires caution,
because they frequently develop CTS and those withNone.

CTS may demonstrate prolongation of DCMAPD
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（2023. 10. 6 received ; 2023. 12. 20 accepted）

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