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The Pain in Neuropathy Study (PiNS): A cross-sectional observational study

determining the somatosensory phenotype of painful and painless diabetic neuropathy

Supplementary materials

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Supplementary methods

Neuropathy screening tools, symptom and function questionnaires

A set of questionnaires assessing the presence of pain, pain intensity, pain distribution and the

psychological and functional impact of pain were either completed before the appointment, or

after the appointment and then returned to the study centre by post .

Patients were asked to keep a pain intensity diary for 7 days, recording pain at 9 am and 9 pm

daily on an 11 point scale, with 0 being no pain and 10 the worst pain imaginable. Study

participants also completed a body map highlighting the distribution of pain.

Toronto Clinical Scoring System (TCSS) is a screening tool for diabetic peripheral

neuropathy, and correlates with diabetic neuropathy severity. The TCSS uses a simplified

neurological examination assessing peripheral sensory perception, deep tendon reflexes, and

the presence of neuropathy symptoms. Deep tendon reflexes scores are graded for each side

as loss, 2; reduced, 1; and normal, 0. The presence of each following neuropathy symptoms is

assigned 1 point: pain, numbness, tingling and weak-ness in the feet, the presence of similar

upper limb symptoms, and the presence of unsteadiness on ambulation. Sensory testing is

performed on the first toe for the following: pinprick sensation, temperature discrimination,

proprioception, light touch, and vibration, performed at the first toe. Responses were rated as

normal or abnormal and were assigned 0 or 1 point, respectively. Scores range from 0 to 19.

The Douleur Neuropathique en 4 Questions (DN4) is a screening tool for neuropathic pain.

DN4 consists of 10 items grouped into four questions: seven items relating to the pain

description (burning, painful cold, electric shocks) and to its associated abnormal sensations

(tingling, pins and needles, numbness, itching) and the other three items relating to a brief

bedside neurological examination in the painful area (touch hypoaesthesia, pinprick

hypoaesthesia, tactile dynamic allodynia). For scoring, 1 is given to each positive and 0 to

each negative item and the total score range 0–10.

The PainDETECT contains nine items, of which seven relate to sensory responses and two to

the temporal and spatial characteristics of the pain pattern. By rating the seven items from

never (0) to very strongly (5) on a category scale and summing these with the scores for

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temporal (−1 to +1) and spatial characteristics (0 or +2), a summary score (minimum −1,

maximum 38) was obtained. A total score of <13 indicates that a neuropathic component is

unlikely, whereas a score of >18 indicates that a neuropathic component is likely.

Brief Pain Inventory (BPI) pain interference and pain severity subscales were used to asses

any type of pain (non-neuropathic and neuropathic) that study participants experience. Pain-

related interference in activities of daily living was assessed using the 7-item Pain

Interference scale of the BPI. The scale assesses pain interference within 7 domains: general

activity, walking, work, relationships, mood, life enjoyment, and sleep. Study participants

score these on a 11 point scale ranging from 0 (does not interfere) to 10 (completely

interferes). The composite score was calculated as the sum of the 7 interference items.

Neuropathic Pain Symptom Inventory (NPSI) is a self-administered questionnaire designed to

evaluate neuropathic pain symptoms. The NPSI was completed for pain in feet and hands. It

evaluates the presence and severity of 10 different neuropathic pain descriptors, each on an

11 point scale where 0 indicates no symptoms and 10 indicates maximal symptoms

experienced. The NPSI also includes 2 temporal items assessing the duration of spontaneous

ongoing pain, and the number of pain attacks on 5-point categorical scales.

Overall Neuropathy Limitation Scale (ONLS) is a scale that measures the limitation of

everyday activities within the upper and lower limbs, It is separated into two scales for the

arm and legs respectively that determines if the activities of daily living are not affected,

affected but not prevented or prevented. A higher score indicates a greater degree of

disability.

Pain Catastrophizing Scale (PCS) assessed the cognitive process by which pain is appraised

in terms of threat and negative consequences. It consists of 13 descriptions of thoughts and

feelings related to pain. Study participants are asked to indicate the degree to which they

experience these on a 5-point rating scale from 0 (not at all) to 4 (always). A high total score

indicates a high level of pain catastrophizing. PCS comprises 3 dimensions: rumination,

magnification, and helplessness. Rumination refers to the patients’ preoccupation with pain;

magnification expresses the exaggerated cognitions of pain as a threat; and hopelessness is

patients’ feelings that they are unable to influence their pain.

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Depression Anxiety Positive-Outlook instrument (DAPOS) was used to measure mood and

consists of 3 subscales. The subscale for depression contains 5 items with scores ranging

from 5 to 25, indicating normal mood to severe depression. The subscale for anxiety contains

3 items, which ranges from 3 to 15, indicating no anxiety to maximal anxiety. The subscale

for positive outlook contains 3 items, which ranges from 3 to 15, indicating poor positive

outlook to good positive outlook.

Pain Anxiety Symptom Scale 20 (PASS-20) assesses pain-related anxiety and is a shortened

version of the PASS. PASS-20 has 20 questions assessing 4 facets of pain-related anxiety:

fearfulness of pain, cognitive anxiety, escape/avoidance, and psychological anxiety. Each

subscale score ranges from 0 (no interference) to 25 (maximum interference). Additionally,

summation of the subscales provides a general measure of pain-related anxiety.

Survey of Autonomic Symptoms (SAS) is an instrument that measures the presence and

impact of autonomic symptoms. It consists of 12 questions that are individually rated on a 6-

point rating scale from 0(not at all) .to 5 (a lot).

Insomnia Severity Index (ISI) measured the study participant’s perception, subjective

symptoms, and consequences of any sleep disturbances. The ISI is composed of 7 items

assessing the severity of sleep onset and sleep maintenance difficulties, satisfaction with

sleep patterns, interference with daily functioning, noticeability of impairment due to sleep

dysfunction, and the degree of distress experienced by the patient. Its content corresponds, in

part, to the diagnostic criteria of insomnia

Short Form 36 of the MOS Outcomes Study (SF-36) assess health-related quality of life. SF-

36 responses were scored in the 8 domains of physical functioning: role–physical, bodily

pain, general health, vitality, social functioning, role–emotional, and mental health. SF-36

scores range from 0 to 100, representing extreme dysfunction/symptom severity to optimal

function, respectively.

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Supplementary figure legends

Supplementary figure 1

a) Scatter plot and mean ± 95% CI of z-scores for Thermal QST parameters in study

participants with no diabetic peripheral neuropathy and those with diabetic peripheral

neuropathy

Unpaired t-tests: *P < 0.05; ** P < 0.01.

WDT- Warm Detection Threshold, CDT – Cold Detection Threshold, TSL - Thermal

Sensory Limen; Cold Pain Threshold; Heat Pain Threshold.

b) Scatter plot and mean ± 95% CI of z-scores for Mechanical QST parameters in study

participants with no diabetic peripheral neuropathy and those with diabetic peripheral

neuropathy.

Unpaired t-tests: * P < 0.05; ** P < 0.01.

MDT- Mechanical Detection Threshold; VDT- Vibration Detection Threshold; MPT-

Mechanical Pain Threshold; MPS- Mechanical Pain Sensitivity; WUR- Wind-up ratio; PPT-

Pressure Pain Threshold

Supplementary figure 2

a) Scatter plot and median (interquartile range) of Warm Sensibility Index for study

participants with no diabetic peripheral neuropathy compared to diabetic peripheral

neuropathy. Mann-Whitney U Test: ** P < 0.01

Scatter plot and median (interquartile range) of Warm Sensibility Index for study participants

with diabetic neuropathy and no neuropathic pain, mild neuropathic pain, moderate/severe

neuropathic pain. Kruskal-Wallis, Dunn's multiple comparison test.

b) Scatter plot and median (interquartile range) of Cold Sensibility Index for study

participants with no diabetic peripheral neuropathy compared to diabetic peripheral

neuropathy. Mann-Whitney U Test: ** P < 0.01

Scatter plot and median (interquartile range) of Cold Sensibility Index for study participants

with diabetic neuropathy and no neuropathic pain, mild neuropathic pain, moderate/severe

neuropathic pain. Kruskal-Wallis, Dunn's multiple comparison test: * P < 0.05.

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Supplementary Table 1

Summary of all drugs used

Data shown as values and percentages and analysed by χ2 squared test of association.

Symbols reflect the differences between the respective groups:

† P < 0.05, †† P < 0.01 between No Neuropathic Pain and Moderate/Severe Neuropathic Pain

# P < 0.05, between Mild Neuropathic Pain and Moderate/Severe Neuropathic Pain

‡‡ P < 0.01 between No Neuropathic Pain and Mild Neuropathic Pain

Supplementary Table 2

Summary of clinical scores, electrophysiological recordings from lower limbs of study

participants with no peripheral neuropathy and diabetic peripheral neuropathy with no

neuropathic pain, mild neuropathic pain, moderate/severe neuropathic pain.

Nerve conduction study interpretations were available for 175 (84%) and IENFD results were

available for 146 study participants (69%).

Data shown as median (interquartile range) and analysed by Kruskal-Wallis, Dunn's multiple

comparison test.

TCSS- Toronto Clinical Scoring System

Symbols reflect the differences between the respective groups:

† P < 0.05, †† P < 0.01 between No Neuropathic Pain and Moderate/Severe Neuropathic Pain

‡‡ P < 0.01 between No Neuropathic Pain and Mild Neuropathic Pain

¶¶ P < 0.01 between No DPN and DPN (across all groups with Neuropathic Pain)

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No Neuropathic

Pain

Mild Neuropathic

Pain

Moderate/Severe

Neuropathic Pain P

Number of participants 80 41 70

Reported drug use 79 39 70

All oral hypoglycaemic agents 65 (82.3%) 30 (76.9%) 48 (73.8%) 0.19

Metformin 64 (81.0%) 29 (74.4%) 45 (69.2%) 0.09

Other Oral hypoglycaemic

(Gliclazide) 33 (41.8%) 13 (33.3%) 16 (24.6%) 0.06

Insulin 31 (39.2%) 17 (41.5%) 34 (52.3%) 0.51

Other agents (Sitagliptin,

Pioglitazone, Exanatide,

Linagliptin)

20 (25.3%) 5 (12.8%) 18 (27.7%) 0.12

Statin 51 (64.6%) 35 (89.7%) ‡‡ 49 (75.4%) # < 0.01

Aspirin 35 (44.3%) 13 (33.3%) 24 (36.9%) 0.37

Anti-Hypertensives 66 (83.5%) 29 (74.4%) 47 (72.3%) 0.12

ACE-I 60 (75.9%) 24 (61.5%) 42 (64.6%) 0.12

Diuretic 16 (20.3%) 15 (38.5%) 17 (26.2%) 0.12

B-blocker 19 (24.1%) 7 (17.9%) 6 (9.2%) † 0.04

Calcium channel blocker 24 (30.4%) 10 (25.6%) 15 (23.1%) 0.52

Thyroxine 10 (12.7%) 3 (7.7%) 5 (7.7%) 0.48

PPI 12 (15.0%) 8 (20.5%) 24 (36.9%) †† 0.02

Supplementary Table 1

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No Diabetic

Neuropathy

No

Neuropathic

Pain

Mild

Neuropathic

Pain

Moderate/

Severe

Neuropathic

Pain

P

Number of participants 18 80 41 70

TCSS

Total Score

1 ¶¶

(0-3)

8

(5-10)

10 ‡‡

(8-13)

11 ††

(8-14) < 0.01

TCSS

Symptom

sub-score

0 ¶¶

(0-1)

1

(1-2)

3 ‡‡

(1-3.5)

3 ††

(2-4) < 0.01

TCSS Examination

sub-score

0 ¶¶

(0-2)

7

(4-8.8)

8

(6-9.5)

8 †

(5.8-11) < 0.01

MRC Sensory Sum

Score 0 ¶¶

6

(2-11)

8

(6-13)

11 ††

(5-18) < 0.01

IENFD (fibres/mm) 5.0 ¶¶

(3.4-6.4)

1.2

(0.4-1.9)

0.8

(0.4-1.7)

1.0

(0.3-1.8) 0.58

Sural nerve

Amplitude (μV) 8.4 ¶¶

(6.3-14.9)

1.0

(0.0-4.0)

0.0

(0.0 -3.5)

1.7

(0.0-5.2) 0.74

Conduction velocity

(m/s)

44.4 ¶¶

(40.6-47.3)

38.9

(33.7-43.2)

41.1

(34.3-45.9)

38.7

(36.3-43.6) 0.78

Peroneal nerve

Amplitude (mV) 4.0 ¶¶

(3.3-5.4)

1.9

(0.5-4.1)

1.4

(0.1-3.5)

0.7

(0.0-2.5) 0.07

Conduction velocity

(m/s)

44.9 ¶¶

(40.4-48.5)

40.1

(35.5-43.3)

39.1

(36.7-43.0)

35.5

(31.8-41.5) 0.20

Supplementary Table 2