A prospective two-center study was conducted at the departments of Neurology and Neurophysiology / Baghdad Teaching Hospital and Al-Imamain Al-Kadhimyain Medical City, Baghdad, Iraq for the period from Sept. 2017 till Feb. 2018. The Iraqi Board for Medical Specialization approved the study (Decision No. 860; Date 12/2/2018). Written informed consent was obtained from all individual participants included in the study.
Twenty-eight patients with ALS (either known cases or they were diagnosed during our workout) comprised 12 females and 16 males aged 55.2 ± 12.312 years (24–69 years) with a duration of illness ranging from 3 to 48 months were studied. Patients with spinal muscular atrophy, progressive muscular atrophy, and Hirayama disease were excluded from the study.
Another 28 healthy subjects comprised of 13 females and 15 males aged 55.5 ± 11.12 years (range 24–65 years) serve as the control group.
Patients with ALS were subjected to a detailed history and clinical neurological examination adopting the El Escorial criteria [13]. Accordingly, nine patients fulfilled the criteria for definite ALS, 19 patients met the criteria for probable ALS, and none of them fulfilled the requirements for possible ALS. They were scored using the revised ALS Functional Rating scale (ALSFRS-R) which denotes 12 items (each of 5 scores from 0 to 4) [14]. Key muscles from the upper and lower extremities were evaluated using the Medical Research Council (MRC) scale against the examiner’s resistance and grading the patient’s strength on a 0 to 5 scale accordingly [15].
Neurophysiologic testing was done using Keypoint (Medtronic, Denmark) and Cadwell (USA) electromyography machines. The motor nerve conduction study of the median, ulnar, tibial, and fibular nerves and sensory nerve conduction study of the median, ulnar, and sural nerves were examined and the F wave latency of either lower limb following the standard methods [16]. The MRC scale and electromyographic activity were studied from the first dorsal interosseous (FDI) muscle. Twenty motor unit action potentials (MUAPs) were analyzed for duration and amplitude during minimal volitional effort. This is assessed by instructing the patient to make only a very gentle (low level) contraction of the muscle under investigation where single (first) MUP can be clearly differentiated on the monitor screen as it achieves a stable and fairly regular firing rate at 5–7 Hz.
A multipoint stimulation (MPS-MUNE) method was used at the asymptomatic side or the less severely affected side (if any) by stimulating the ulnar nerve and recording from the abductor digiti minimi (ADM). The ulnar nerve was stimulated at three sites; 2 cm proximal to the wrist crease, 4 cm proximal to the first site, and 1 cm proximal to the ulnar groove at the elbow. At each side, we adjust the intensity at which we obtain the all or non-potential response which represent the single motor unit potential (SMUP). After recording one SMUP with a minimum amplitude of ≥ 25 μV, the stimulus intensity increased gradually by 4 mA for 10 times to have 10 SMUP at each site. The number of stimulations at each site should not be less than 4 and can be up to 10. We did this procedure for each of the 3 sites of the nerve for each patient.
In severely affected patients with less than 10 SMUPs, as many as possible of SMUPs were recorded. MUNE can be calculated by dividing the supramaximal CMAP amplitude by the average amplitude of the ~ 10 SMUPs.
The CMAP amplitude recorded from ADM muscle was measured from baseline to negative peak, and the CMAP with the highest amplitude is recorded.
Statistical analysis
Statistical analysis was performed using IBM-SPSS (statistical package for Social Sciences) version 25. Normal distribution of the data was assessed with the Kolmogorov-Smirnov test and variance homogeneity were evaluated with the Levene test. An independent t test was used to analyze the difference between ALS patients and control groups concerning age, MUNE, CMAP amplitude, and SMUP. Chi-square test tests the association between gender with disease progression and age with disease progression.
Pearson’s correlation examined the relationship between reduced FDI clinical function (as evaluated by the MRC scale and number of MUs calculated by MUNE); the relation between the MRC score and CMAP amplitude values, and the relation between disease duration, MUNE, MUAP parameters in FDI and SMUP.
ROC curve was used in the context of discrimination between MUNE and CMAP amplitude in detecting MU loss. According to this curve, the area under the curve (AUC), the sensitivity and specificity, and cut-off values were calculated.
The p value of ≤ 0.05 was considered statistically significant.