Electrophysiological characteristics of patients with nitrous oxide abuse

Figures & data

Table 1. Age and gender of patients

Patients	N2O abuse (n = 20)	GBS-AIDP (n = 19)	GBS-AMAN (n = 18)	DPN (n = 20)	Control (n = 20)
Age (years)	21.1 ± 4.1*	51.3 ± 16.6	56.5 ± 13.4	62.2 ± 9.9	22.2 ± 4.0
Male: Female	14: 6	10: 9	8: 10	13:7	14:6

GBS: Guillain-Barré syndrome; AIDP: acute inflammatory demyelinating polyradiculoneuropathy; AMAN: acute motor axonal neuropathy; DPN: diabetic peripheral neuropathy. Data were presented as mean ± SD. *: P < 0.001 vs. AIDP or AMAN or DPN.

Table 2. Detailed characteristics of patients with nitrous oxide abuse

Case	Age (years)	Gendar	Duration (months)	Frequency	Days between onset symptoms and EDX	Presenting physical symptoms
1	22	Male	6	3–4 canisters at a time and 2–3 times a week	10	Intermittent paraesthesia and reduced power
2	20	Male	24	15–20 N2O bulbs at a time and 2–3 times per month	30	Progressive weakness and numbness, especially in both feet
3	24	Male	36	4–5 canisters twice a week	30	Symmetrical weakness and paraesthesia in both legs
4	18	Male	12	No data provided	30	Ascending distal numbness, and weakness
5	18	Male	36	2–3 times a week and more than 10 canisters each time	60	Ascending numbness and hypoesthesia, a tendency to fall when walking
6	16	Male	24	The maximum was 12 canisters at a time but not always	60	A gradual worsening of tingling sensation in feet and poor balance
7	22	Female	24	2 canisters at a time and 4–5 times a week	30	Gradual lower-extremity weakness
8	21	Male	24	No data provided	17	Numbness, tingling
9	17	Female	18	7–8 canisters/week	15	Numbness in the feet and progressive weakness in the lower extremities
10	31	Female	6	2–4 canisters daily	60	Numbness, paresthesias, weakness
11	22	Male	6	4–5 canisters daily	60	Weakness, foot drop, numbness
12	18	Female	12	No data provided	15	Tingling, numbness
13	29	Male	12	Each time 10–20 canisters, a total of about 100 canisters	90	Difficulty moving
14	21	Female	36	3 canisters at a time and 3 times a week	60	Paresthesias, difficulty walking
15	20	Male	6	No data provided	10	Limbs numbness and gait instability
16	22	Male	12	No data provided	7	Bilateral numbness and weakness in both lower limbs
17	26	Male	2	6–7 N2O bulbs at a time and 2–3 times a week	15	Paresthesias
18	16	Male	1	3 canisters per day	7	Distal limb weakness was evident with sensory ataxia
19	16	Female	3	800 N2O bulbs per day	20	Difficulty walking, falled
20	23	Male	No data provided	2–3 canisters/week	15	Numbness and weakness

EDX: electrodiagnosis

Table 3. Abnormal rate of electrophysiological parameters in patients diagnosed with N₂O abuse (n = 20)

Electrophysiological parameters	Motor nerve				Sensory nerve
	Median	Ulnar	Fibular	Tibial	Median	Ulnar	Sural
DML	6 (30.0)	6 (30.0)	11 (55.0)	11 (55.0)
MNCV	5 (25.0)^*#	3 (15.0) ^*#	16 (80.0)	14 (70.0)
Amplitude of CAMP	3 (15.0)^*#	0^*#	13 (65.0)	14 (70.0)
SNCV					11 (55.0)	11 (55.0)	5 (25.0)
Amplitude of SNAP					0	0	0

The data in parenthesis were indicative of %. DML: distal motor latency; CAMP: compound muscle action potential; MNCV: motor nerve conduction velocity; SNCV: sensory nerve conduction velocity; SNAP: sensory nerve action potential. *P < 0.01 with fibular nerve; #P < 0.01 with tibial nerve.

Figure 1. Comparison of DML extension in the limbs of patients with nitrous oxide abuse. Percentage of the extended DML was calculated as described in the methods. Vertical axis: Extent of prolonged distal latency of motor nerve (%), horizontal axis: nerves examined. DML: distal motor latency. *P < 0.05, N = 20

Figure 2. Comparison of MNCV decrease, CMAP amplitude decrease, and SNCV decrease in the limbs of patients diagnosed with nitrous oxide abuse. Percentage of the extended MNCV decrease (A), CMAP amplitude decrease (B), and SNCV decrease (C) was calculated as described in the methods. Vertical axes: Extent of MNCV decrease (A), CMAP amplitude decrease (B), and SNCV decrease (C); horizontal axes: nerves examined. MNCV: motor nerve conduction velocity; CMAP: compound muscle action potential; SNCV: sensory nerve conduction velocity; AE: above elbow; BE: below elbow; BF: below fibular head. N = 20. There was no difference in the extent of MNCV decrease, SNCV decrease, and CMAP amplitude decrease between the upper and lower limb nerves in the patients with nitrous oxide abuse

Table 4. Electrophysiological parameters in controls and patients diagnosed with N₂O, GBS-AIDP, GBS-AMAN and DPN

Parameters	GBS-AIDP (n = 19)	N2O (n = 20)	GBS-AMAN (n = 18)	DPN (n = 20)	Control (n = 20)
Median DML (ms)	9.7 ± 6.4*	3.8 ± 0.8^*#	3.8 ± 0.5*	4.6 ± 1.7^#*	3.0 ± 0.3
Median MNCV (m/s)	36.2 ± 14.3*	50.6 ± 6.4^*#	50.0 ± 3.6*	48.7 ± 5.9*	62.5 ± 6.9
dCMAP (mV, wrist)	6.3 ± 4.5*	12.0 ± 7.1^*#	7.1 ± 4.3*	9.0 ± 4.9*	17.7 ± 4.5
pCMAP (mV, elbow)	4.6 ± 3.9*	10.6 ± 7.1^*#	5.9 ± 3.3*	8.4 ± 4.7*	17.4 ± 4.5
Median SNCV (m/s, digitus medius)	35.1 ± 12.0*	50.6 ± 5.1^*#$	48.8 ± 14.1*	41.1 ± 8.7	57.0 ± 4.8
Median SNCV(m/s, palmar)	36.5 ± 12.3*	50.0 ± 4.4^*#	52.6 ± 17.8	39.8 ± 10.9	60.9 ± 5.8
Median SNAP(µV, digitus medius)	2.7 ± 1.0*	10.2 ± 6.3^*#$	7.3 ± 4.2*	4.9 ± 4.7	15.8 ± 9.5
Median SNAP(µV, palmar)	8.9 ± 6.9*	25.2 ± 13.6^#	20.9 ± 8.0	15.4 ± 15.4	32.3 ± 16.1
Ulnar DML (ms)	3.7 ± 1.0*	2.8 ± 0.4^*#	2.9 ± 0.4*	2.9 ± 0.4^#*	2.3 ± 0.2
Ulnar MNCV (m/s, wrist-BE)	35.2 ± 14.2*	52.3 ± 6.2^*#	51.3 ± 7.4*	48.6 ± 7.4*	62.2 ± 5.1
Ulnar MNCV (m/s, BE-AE)	32.72 ± 10.9*	56.2 ± 7.7^*#	49.4 ± 12.0*	48.4 ± 8.5*	64.8 ± 10.5
dCMAP (mV, wrist)	7.5 ± 4.6*	13.1 ± 4.0^#&$	3.8 ± 2.6*	9.2 ± 3.5*	12.5 ± 3.3
pCMAP (mV, BE)	5.3 ± 4.5*	11.2 ± 4.2^#&$	2.8 ± 2.1*	8.3 ± 3.6*	12.3 ± 2.9
pCMAP(mV, AE)	5.3 ± 4.5*	11.7 ± 3.9^#&$	2.2 ± 1.5*	8.2 ± 3.3*	12.6 ± 3.0
Ulnar SNCV(m/s, ms)	33.7 ± 8.8*	46.9 ± 6.3^*#$	53.7 ± 11.8	39.7 ± 6.5	51.6 ± 4.1
Ulnar SNAP (µV)	2.5 ± 1.6*	7.5 ± 4.0^*#$	7.8 ± 2.5	4.0 ± 2.7	10.2 ± 4.6
Tibial DML (ms)	10.2 ± 3.4*	5.1 ± 1.0^*#	5.8 ± 1.1*	4.8 ± 1.2^#*	3.4 ± 0.4
Tibial MNCV (m/s)	32.5 ± 11.2*	37.8 ± 6.1*	37.7 ± 5.7*	34.0 ± 7.6*	49.9 ± 3.6
dCMAP (mV, ankle)	2.6 ± 2.7*	3.8 ± 3.9*	2.2 ± 1.9*	4.6 ± 4.1*	21.8 ± 6.8
pCMAP (mV, popliteal fossa)	2.0 ± 2.8*	3.7 ± 4.0*	1.8 ± 1.8*	3.1 ± 3.0*	19.0 ± 6.3
Fibular DML (ms)	9.0 ± 3.6*	5.7 ± 1.3^*#	5.3 ± 1.1*	4.4 ± 1.2^#	3.8 ± 0.6
Fibular MNCV (m/s)	31.3 ± 8.4*	36.7 ± 5.6*	38.7 ± 5.1*	36.7 ± 8.1*	50.4 ± 3.5
dCMAP(mV, ankle)	1.2 ± 1.9*	3.8 ± 3.8*	2.4 ± 1.6*	2.3 ± 2.2*	8.9 ± 4.5
pCMAP (mV, BE)	1.5 ± 2.1*	3.1 ± 3.4*	1.4 ± 0.6*	2.0 ± 1.7*	8.2 ± 4.3
Sural SNCV (m/s)	36.0 ± 10.5*	44.6 ± 8.5^#	45.2 ± 5.0	39.0 ± 8.3	48.9 ± 5.3
Sural SNAP (µV)	3.7 ± 1.5*	10.1 ± 5.2^#$	12.4 ± 6.0	2.7 ± 2.2	13.8 ± 8.0

Data were expressed as mean ± SD. *P < 0.05 vs. Control; ^#P < 0.05 vs. AIDP; ^&P < 0.05 vs. AMAN. ^$P < 0.05 vs. DPN. GBS: Guillain-Barré syndrome; AIDP: acute inflammatory demyelinating polyradiculoneuropathy; AMAN: acute motor axonal neuropathy; DPN: diabetic peripheral neuropathy. AE: above elbow; BE: below elbow; DML: distal motor latency; MNCV: motor nerve conduction velocity; SNCV: sensory nerve conduction; dCMAP: compound muscle action potential after distal stimulation; pCMAP: compound muscle action potential after proximal stimulation; SNAP: sensory nerve action potential.