Role of neuro-sonography of peripheral nerves as a diagnostic and a differentiation tool of amyotrophic lateral sclerosis

Motor neuron disease is a heterogeneous group of progressive neurodegenerative disorders, most common of which is amyotrophic lateral sclerosis (ALS). There are many clinical and radiological criteria to diagnose amyotrophic lateral sclerosis and to differentiate it from other motor neuron disease and neurodegenerative disorders. Neuro-sonography is one of the easily applied tools to diagnose and differentiate ALS. ALS diagnosis is delayed up to 3 years according to some authors due to the wide differential diagnosis, with cervical degeneration being a common misdiagnosis. The objective of this study was to evaluate the role of neuro-sonography in diagnosis and differentiation of amyotrophic lateral sclerosis from other causes of progressive mixed upper and lower motor neuron lesion. A total neuro-sonography score at a cut-off point (≤ 127) predicted patients with ALS, with good (85%) accuracy, sensitivity = 73% and specificity = 83% (p < 0.01) and Lt median arm score at a cut-off point (≤ 6) predicted patients with ALS, with good (88%) accuracy, sensitivity = 86% and specificity = 86% (p < 0.01) and the median nerve at the arm level was the most sensitive and specific nerve to predict patients with ALS. Neuro-sonography of peripheral nerves is a recent, noninvasive, accessible technique that can be used in early diagnosis of ALS.


Background
Neuro-sonography is an emerging neuro-imaging modality that allows evaluation of multiple peripheral nerves in a short time window as it often shows multifocal enlargement of nerves in demyelinating neuropathies [1]. Inflammatory demyelinating and axonal neuropathies may have distinctive sonographic patterns of nerve enlargement and appear to be influenced by treatment [2]. Ultrasonography of the peripheral nervous system is a relatively young area of interest in neurology, although it was already reported in the radiological literature in the 1980s [3]. It allows peripheral nerves to be visualized with excellent resolution and has proved to be reliable, effective, noninvasive and well tolerated. As many peripheral nerves run a superficial course, they are easily accessible to sonography, even very small nerves and fascicular patterns can be studied. Furthermore, nerves may be examined over a long course in a few minutes (e.g., the median nerve from wrist to axilla) [3]. Nerve sonography has been applied to amyotrophic lateral sclerosis (ALS) demonstrating evidence of both nerve root and distal peripheral nerve atrophy [4]; this offers potential for ultrasound-based differentiation of ALS and ALS-mimicking disorders characterized by enlarged nerves [5].

Open Access
The Egyptian Journal of Neurology, Psychiatry and Neurosurgery

Methods
An observational case-control study with 90 participants, 30 of them suffering from amyotrophic lateral sclerosis presenting at our hospitals, and 30 subjects with cervical degeneration diagnosed by MRI cervical spine who presented to general neurology and neuromuscular clinics of our hospitals in the period between April 2018 till April 2020 and 30 healthy controls with unremarkable neurological history and examination.
• Sex: males and females.
For the cases: • The diagnosis of ALS according to El Escorial World Federation of Neurology Criteria for the Diagnosis of ALS [6]. • Subjects with symptoms and signs of cervical disc degeneration diagnosed by MRI cervical spine and should be for a period of 3 months at least.
For the controls: • The control group consisted of 30 healthy volunteers with age and sex matched to cases.
Exclusion criteria: • Subjects with metabolic diseases complicated with neurological symptoms such as diabetes mellitus, chronic kidney disease, inflammatory liver disease, subjects taking drugs known to affect peripheral nerves, etc. • Subjects with congenital neurological involvement.
Cross-sectional area of the following nerves was measured: the median nerve-at the carpal tunnel, at the mid-level of the forearm and the upper arm; the ulnar nerve-at the Guyon's canal, at the mid-level of the forearm and the upper arm; the radial nerve at the spiral grove; the posterior tibial nerve at the tarsal tunnel, and the tibial nerve at the popliteal fossa.

Statistical analysis
Data entry, processing and statistical analysis was carried out using MedCalc ver.18.11.3 (MedCalc, Ostend, Belgium). Tests of significance (ANOVA, Chi-square tests, Pearson's correlation, and ROC-curve analysis) were used. Data were presented and suitable analysis was done according to the type of data (parametric and nonparametric) obtained for each variable. P-values less than 0.05 (5%) was considered to be statistically significant. P > 0.05: non-significant (NS), P < 0.05: significant (S), P < 0.01: highly significant (HS).

Results
Ninety participants were included in this study where the mean age of all subjects was (46.4 ± 14.8) years. Regarding gender of the patients, the majority (63.3%) of patients were males, while (36.7%) were females. By using ROC-curve analysis, total neuro-sonography score at a cut-off point (≤127) predicted patients with ALS, with good (85%) accuracy, sensitivity of 73% and specificity of 83% (p < 0.01).

Clinical data
This table shows that; the mean age of all patients was (46.4 ± 14.8) years. Regarding gender of the patients, the majority (63.3%) of patients were males, while (36.7%) were females (Table 1).
Regarding site of onset, 13.3% of patients had bulbar and lumbar onset, 6.7% had cervical onset, 36.7% had LL onset, and 30% had UL onset.
Regarding basic clinical data, 43.3% of patients were smokers, 26.7% had positive consanguinity and 33.3% had positive family history (Table 3). Regarding neurological data, the average age of onset was 42.4 ± 15.4 years, the average disease duration was 1.8 ± 1.4 years, the average ALS-FRS scale was 37.2 ± 8.4.
Comparative study between the 3 groups revealed highly significant increase in age in cervical group, compared to other groups (p = 0.011) (Fig. 1).
Comparative study between the 3 groups revealed nonsignificant difference as regards sex of patients (p > 0.05) ( Table 5, Fig. 2).

Neuro-sonography data
Comparative study between the 3 groups revealed highly significant decrease in total UL, LL and overall neuro-sonography score measurements in ALS group, compared to other groups (p < 0.01, respectively) ( Table 6; Figs. 3, 4, 5).
Pearson's correlation analysis shows that disease duration had a highly significant negative correlation with total neuro-sonography score in (cervical group) (p = 0.0016) ( Table 7; Fig. 6).
Pearson's correlation analysis shows that all factors had a non-significant correlation (Table 9).
Pearson's correlation analysis shows that age had a non-significant correlation with total neuro-sonography score in (control group) (p > 0.05) ( Table 10).
The median and ulnar nerves are the most affected nerves in ALS patients as shown in Table 11, Fig. 7.

Discussion
The primary objective of this study is to assess the neuro-sonography for diagnosis and differentiation of amyotrophic lateral sclerosis. This is a conventional   case-control study conducted on 90 patients attending to Ain-Shams University Hospitals. To our knowledge, this is the first comparative neurosonography study to assess differentiation of ALS and cervical degeneration subjects presented with similar clinical picture.
In our study, we also worked on the neuro-sonography cross-sectional area of both lower limbs' peripheral nerves in addition to both upper limbs, which is scarcely preceded by other studies.
Peripheral nerve atrophy as reported on group-level in most of the ultrasound studies comparing ALS and healthy controls most likely reflects axonal degeneration in ALS, but correlation studies between ultrasound and histopathology are thus far lacking.
Our findings goes in accordance with other authors who also found out that ALS could be prevalent in specific age group with specific subtypes and gender; ALS is characterized by a sexual dimorphism, the most obvious being the higher risk of developing the disease in men [7]. More subtle differences between the two sexes have been reported both in ALS preclinical models and in humans [8].
Age is the strongest risk factor of ALS as found out by [7], 8]. It has been found out that the median age at onset is 67.1 years, Bulbar phenotype was correlated with older age, where women were more affected than men at increasing ages, while classic phenotype, on the contrary, was associated with younger age, where the risk in men increased with age, PUMN was correlated with younger age, flail arm phenotype was associated with male sex and less strongly with younger age and finally, respiratory phenotype was correlated with male sex and showed a trend toward a higher frequency in older age [9].
The spread of lesions across the CNS in ALS has been explained either as a neuroanatomical contiguous propagation in the upper and lower motor neurons, with random onset in discrete body regions [10] or as a prion-like propagation, with either contiguous or noncontiguous diffusion [11] or, finally, as a sequential pattern of spread of TDP43 pathology with a corticofugal mechanism [12].
Further aspects that have contributed to the large variance of the available nerve ultrasound data include the lack of standardized imaging protocols and ratings.
The mean cross-sectional areas of the radial nerves reported by [15] were as follows: at 4 cm at the lateral epicondyle of the humerus (4 cm), 5.14 ± 1.24 mm 2 ; and  at mid-humerus (midpoint between the elbow crease and axilla), 5.08 ± 1.23 mm 2 Regarding tibial nerve at the popliteal fossa 19 mm 2 ± 6.9, tibial nerve at the level of the medial malleolus 12.7 mm 2 ± 4.5, common peroneal nerve at the popliteal fossa 9.5 mm 2 ± 4, common peroneal nerve fibular head 8.9 mm 2 ± 3.2, sural nerve 3.5 mm 2 ± 1.4 [16]. Schreiber et al., compared nerve CSA between ALS and controls, similarly reporting peripheral nerve atrophy in ALS affecting the ulnar nerve at the wrist, the median nerve at the forearm, and the ulnar, median and radial nerves in the upper arm [17].
However, not all studies are in agreement on which nerves are reduced at which sites. One group reported pronounced atrophy of the distal ulnar nerve [18]; Noto et al. did not find a reduction of ulnar nerve size in ALS [19] Mori et al., also found that the cervical root and peripheral nerve CSA atrophy seem thereby to occur in all ALS disease phenotypes independent of the degree of UMN or LMN involvement or from the site of disease onset [20].
It was proposed that CSA enlargement of the four nerves yielded an optimal combined sensitivity and specificity to discriminate between ALS and MMN. Goedee et al. later stated that CSA enlargement of even just two nerves should be accurate enough to distinguish between the two diseases [21].
The total neuro-sonography score at a cut-off point (≤127) predicted patients with ALS with good (85%) accuracy, sensitivity of 73% and specificity of 83% (p < 0.01). This shows the significance of neuro-sonography as a diagnostic and differentiation tool in neurodegenerative diseases and neuromuscular diseases as well, and this goes in agreement with other authors such as [22], who found out that the cross-sectional area of the median nerve in the mid-arm was smaller in the ALS group than    controls (10.5 mm 2 vs 12.7 mm 2 , p = 0.0023). This also goes in accordance with [18] who found out that compared with controls, ALS patients had significant, distally pronounced reductions of ulnar CSA (forearm/ wrist level) across all disease groups, except for PLS and median nerve CSA (forearm/wrist level) did not differ between controls and ALS while ulnar nerve ultrasound in ALS subgroups revealed significant differences in distal CSA values, which suggests it has value as a marker of LMN involvement. Its potential was particularly evident in the UMND and PLS groups, which can be hard to separate clinically.

Conclusions
Neuro-sonography is an evolving and promising tool in diagnosis and differentiation of amyotrophic lateral sclerosis and other neurodegenerative such as cervical degeneration and it is recommended as an ancillary tool to aid in history and clinical examination.