Stimulated jitter with concentric needle in 42 myasthenia gravis patients

Forty-two confirmed myasthenia gravis patients, being 22 males (aged 45.6±17.2 years-old) were studied. Jitter was expressed as the mean consecutive difference (MCD).

Results:

MCD in extensor digitorum was 61.6 µs (abnormal in 85.7%) and in frontalis 57.3 µs (abnormal in 88.1%). Outliers represented 90.5% for extensor digitorum and 88.1% for frontalis. At least one jitter parameter was abnormal in 90.5% of the combined studies. Acetylcholine receptor antibody was abnormal in 85.7% of the cases.

Conclusions:

Stimulated jitter recordings measured from muscles using concentric needle electrode can be used for myasthenia gravis diagnosis with high sensitivity. Extensive normative studies are still lacking and, therefore, borderline findings should be judged with great caution.

jitter; myasthenia gravis; concentric needle electrode; Extensor Digitorum; Frontalis; single-fiber electromyography

Muscle	MCD					ASFAP
Muscle	n	Mean (µs)	Range	ab^∗ (%)	n	Mean (µs)	Range	ab^∗∗ (%)
ED	42	61.6	12.4221 µs	85.7	1,209	55.5	6.3299 µs	90.5
FR	42	57.3	12.3124 µs	88.1	1,327	48.4	6.6268 µs	88.1
ED or FR				90.5				90.5

Parameters	Generalized	Abnormal (%)	Ocular	Abnormal (%)
n	36		6
Age at debut	43.8 (2182)		56.7 (2778)
Symptoms duration	82.4 months (2288)		34.3 months (293)
Mean MCD ED^∗	65.6 µs (12.4221)	88.9	37.2 µs (17.664.9)	66.7
Mean MCD FR^∗	58.7 µs (12.3124)	88.9	48.7 µs (16.780.6)	83.3
Outliers ED^∗		91.7		83.3
Outliers FR		88.9		83.3
Some blocking ED^∗		25.8		16.0
Some blocking FR^∗		25.3		27.1
AChRAb nmol/L^∗	12.63 (0.1831.3)	88.8	3.49 (1.536.32)	66.7
RNS (1-4)^∗∗		94.4		66.7
Thymectomy^∗∗	16/36 (44.4%)		0/36 (0%)

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[1] Correspondence: João Aris Kouyoumdjian; Rua Luiz Antônio da Silveira 1.661; 15025-020 São José do Rio Preto SP - Brasil; E-mail: jaris@terra.com.br

Case	MCD		Outliers		AChRAb	RNS-w	MGFA-w
Case	ED	FR	ED^∗	FR^∗	nmol/L	ab ≥10%	Class
1	24.4	23.6	16.7	23.3	<0.10	n	I
2	30.7	112	50	96.7	16.5	ab	IIb
3	29.2	50.1	36.7	96.7	15.5	ab	V
4	21.5	85.6	10	93.3	7.35	ab	IVb
5	48.8	38.5	64.3	60.7	6.32	ab	I
6	104	124	72.2	100	15.7	ab	IIIa
7	29.6	114	40	100	11.61	ab	IIb
8	23.6	14.4	10	0	<0.10	ab	IIIa
9	78.9	75.1	90.6	90.6	6.48	ab	IVa
10	35.6	62.7	55.2	94.1	3.82	ab	IIIb
11	90.2	65.2	96	97.1	4.98	ab	IIIb
12	64.9	80.6	76.7	85.3	3.44	ab	I
13	17.6	16.7	8.8	9.1	1.53	n	I
14	79.2	68.6	89.7	87.5	18.5	ab	IIb
15	12.4	12.3	0	0	<0.10	n	IIb
16	79.8	74.2	96.8	88.2	15.8	ab	V
17	221	54.6	100	83.9	16.6	ab	IVa
18	39	57.7	66.7	81.8	15.4	n	IIIb
19	55.2	58.3	78.6	79.4	3.1	ab	IIIa
20	144	77.6	84.6	93.9	22.3	ab	IVa
21	79.3	91.2	91.2	97.8	2.22	ab	V
22	157	88	100	96.9	10.8	ab	V
23	121	57.9	93.7	83.3	0.18	ab	V
24	34.4	23.3	48.6	18.2	1.47	ab	IVa
25	45	54.6	63.6	67.5	2.7	ab	I
26	22	15.5	3.3	3.3	12.5	ab	IVa
27	40.6	45.5	67.6	87.1	6.8	ab	V
28	40.7	64.3	63.6	83.3	26.0	ab	IIIa
29	95.2	46.5	100	63.3	28.0	ab	IVa
30	75.4	50.1	96.7	63.3	31.3	ab	IVb
31	31.6	38.8	45.5	63.3	16	ab	IIb
32	57.9	33.2	60	46.7	<0.10	ab	IIIa
33	28.1	29.8	26.7	26.7	19.5	ab	V
34	17	15.7	0	3	<0.10	ab	IVa
35	22.3	77.9	23.3	77.8	<0.10	ab	I
36	74.6	54	81.2	78.8	12.7	ab	IVa
37	70.2	70.8	90	90.9	17.9	n	V
38	60.4	74.8	70	85.2	2.91	ab	IVa
39	43.7	43.7	65.6	59.4	20.6	ab	IIIb
40	116	59.9	100	90	8.54	ab	IVa
41	56.4	55.3	75	76	6.56	ab	V
42	67.6	45.1	86.7	66.7	6.59	ab	IVa
Limit	22.6 µs	21.5 µs	30 µs	30 µs
Ab	85.7%	88.1%	90.5%	88.1%	85.7%	88.0%