Differences in F-Wave Characteristics between Spinobulbar Muscular Atrophy and Amyotrophic Lateral Sclerosis

Unique clinical and electrophysiological features in the peripheral nerve system in patients with sialidosis - a case series study

BACKGROUND

To investigate the peripheral nervous system involvement in S sialidosis with typical features of myoclonus, seizure, and giant waves in somatosensory evoked potentials suggesting hyperexcitability in the central nervous system.

METHODS

The clinical presentation of patients with genetically confirmed sialidosis was recorded. Neurophysiological studies, including nerve conduction studies (NCSs), F-wave studies, and needle electromyography (EMG), were performed on these patients.

RESULTS

Six patients (M/F: 2:4) were recruited. In addition to the classical presentation, intermittent painful paresthesia was noted in four patients, and three of whom reported it as the earliest symptom. In the NCSs, one patient had reduced compound muscle action potential amplitudes in the right ulnar nerve, while another patient had prolonged distal motor latency in the bilateral tibial and peroneal nerves. Prolonged F-wave latency (83.3%), repeater F-waves (50%), and neurogenic polyphasic waves in EMG (in 2 out of 3 examined patients) were also noted. Interestingly, a very late response was noted in the F-wave study of all patients, probably indicating lesions involving the proximal peripheral nerve or spinal cord.

CONCLUSION

In addition to the central nervous system, the peripheral nervous system is also involved in sialidosis, with corresponding clinical symptoms. Further study on these phenomena is indicated.

Evaluation of F wave and split hand index in patients with amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is characterized by gradual disturbance of both upper and lower motor neurons (LMN). In ALS, muscle wasting favors the abductor pollicis brevis (APB) and first dorsal interosseous (FDI), with relative preservation of abductor digiti minimi (ADM).

Objectives

To interpret F wave changes in the context of upper and LMN dysfunction and the differences in dysfunction between spinal motoneurons innervating the APB and ADM.

Patients and methods

Forty-four subjects were studied (22 patients with ALS and 22 controls). F wave was elicited by 50 electrical stimuli from the median and ulnar nerves, and the split hand index (SHI) was measured.

Results

F latency mean, median, and maximum and F amplitude mean, median, and maximum F/M amplitude ratio were increased in patients with versus those without pyramidal signs. Limb-onset ALS patients showed the biggest reduction in SHI. The APB muscle of patients with no detectable wasting and upper MN (UMN) signs showed reduced F wave persistence, mean F wave latency and amplitudes, increased index repeater neuron and index F repeater, and mean F/M amplitude ratio.

Conclusion

There is enhanced segmental motoneuronal excitability following UMN dysfunctions. SHI appears to be a diagnostic biomarker for ALS. Abnormal F parameters recorded from APB muscle can distinct patients with ALS from the normal controls to a greater extent than do the APB/ADM and FDI/ADM compound muscle action potential amplitude ratios.

Clinical and Physiological Significance of F-Wave in Spinocerebellar Ataxia Type 3

Objective: To evaluate the characteristics of F-wave in spinocerebellar ataxia type 3 (SCA3) patients and preclinical carriers of SCA3 gene mutation (PreSCA3), and explore the relationship between disease severity and F-wave parameters and evaluate F-wave parameters as potential biomarkers for monitoring of disease progression in SCA3. Methods: We performed F-wave recordings in median, ulnar and tibial nerves of 39 SCA3 patients, 20 PreSCA3, and 27 healthy controls, and compared F-wave parameters between them. Results: In all nerves studied, the mean F-wave amplitude, maximum F-wave amplitude, and F/M amplitude ratio were significantly increased in the SCA3 patients in comparison with the normal controls. And the minimal F-wave latency of SCA3 patients was significantly prolonged and the F-wave persistence (%) was significantly decreased in the median nerve. For the PreSCA3, the maximum F-wave amplitude was significantly higher than normal controls for both median, ulnar, and tibial nerves. The mean F-wave amplitude and F/M amplitude ratio in all nerves were comparable between PreSCA3 and normal controls. The frequency of giant F-wave and frequency of patients with giant F-wave were similar between PreSCA3 and SCA3. The values of F/M amplitude ratio in both median, ulnar, and tibial nerves were correlated positively with disease severity and disease duration. Conclusion: Significant F-wave abnormalities occur in patients with SCA3, even in PreSCA3. F-wave may therefore reveal subclinical alterations and provide objective parameters for evaluating the progression of SCA3.

The French national protocol for Kennedy's disease (SBMA): consensus diagnostic and management recommendations

Background

Kennedy’s disease (KD), also known as spinal and bulbar muscular atrophy (SBMA), is a rare, adult-onset, X-linked recessive neuromuscular disease caused by CAG expansions in exon 1 of the androgen receptor gene (AR). The objective of the French national diagnostic and management protocol is to provide evidence-based best practice recommendations and outline an optimised care pathway for patients with KD, based on a systematic literature review and consensus multidisciplinary observations.

Results

The initial evaluation, confirmation of the diagnosis, and management should ideally take place in a tertiary referral centre for motor neuron diseases, and involve an experienced multidisciplinary team of neurologists, endocrinologists, cardiologists and allied healthcare professionals. The diagnosis should be suspected in an adult male presenting with slowly progressive lower motor neuron symptoms, typically affecting the lower limbs at onset. Bulbar involvement (dysarthria and dysphagia) is often a later manifestation of the disease. Gynecomastia is not a constant feature, but is suggestive of a suspected diagnosis, which is further supported by electromyography showing diffuse motor neuron involvement often with asymptomatic sensory changes. A suspected diagnosis is confirmed by genetic testing. The multidisciplinary assessment should ascertain extra-neurological involvement such as cardiac repolarisation abnormalities (Brugada syndrome), signs of androgen resistance, genitourinary abnormalities, endocrine and metabolic changes (glucose intolerance, hyperlipidemia). In the absence of effective disease modifying therapies, the mainstay of management is symptomatic support using rehabilitation strategies (physiotherapy and speech therapy). Nutritional evaluation by an expert dietician is essential, and enteral nutrition (gastrostomy) may be required. Respiratory management centres on the detection and treatment of bronchial obstructions, as well as screening for aspiration pneumonia (chest physiotherapy, drainage, positioning, breath stacking, mechanical insufflation-exsufflation, cough assist machnie, antibiotics). Non-invasive mechanical ventilation is seldom needed. Symptomatic pharmaceutical therapy includes pain management, endocrine and metabolic interventions. There is no evidence for androgen substitution therapy.

Conclusion

The French national Kennedy’s disease protocol provides management recommendations for patients with KD. In a low-incidence condition, sharing and integrating regional expertise, multidisciplinary experience and defining consensus best-practice recommendations is particularly important. Well-coordinated collaborative efforts will ultimately pave the way to the development of evidence-based international guidelines.

F wave, A wave, H reflex, and blink reflex

Late responses include F waves, A waves, H reflex, and the blink reflex. These responses help enhance routine nerve conduction studies. Despite the use of F waves in multiple clinical applications, their studies can technically challenge even the most experienced electromyographers. They vary in latency, amplitude, and configuration, whereas A waves show no change in latency or morphology. Electrical stimulation of the supraorbital branch of the trigeminal nerve on one side results in a reflexive activation of the facial nucleus causing contraction of the orbicularis oculi muscle, short latency R1 ipsilaterally, and long latency R2 bilaterally. F waves can help determine the presence of a polyneuropathy. A waves can reflect axonal damage. H reflexes provide nerve conduction measurements along the entire length of the nerve, demonstrating abnormalities in neuropathies and radiculopathies. Abnormalities in the blink reflex can suggest the presence of an acoustic neuroma or a demyelinating polyneuropathy, which can affect the cranial nerves. This reflex, which also needs appropriate technical expertise, helps to assess cranial nerves V and VII along with their connections in the pons and medulla. The blink reflex, the electrical version of the corneal reflex, represents a polysynaptic reflex.

A Retrospective Study of the Characteristics and Clinical Significance of A-Waves in Amyotrophic Lateral Sclerosis

A-wave was observed in patients with motor neuron disease (1). However, data on the characteristics and clinical significance of A-waves in patients with amyotrophic lateral sclerosis (ALS) have been scarce. The F-wave studies of 83 patients with ALS and 63 normal participants which were conducted previously at the Department of Neurology in Peking Union Medical College Hospital were retrospectively reviewed to determine the occurrence of A-waves in ALS. A-waves occurred more frequently in ALS patients than in normal controls. For the median and peroneal nerves, the frequencies of nerves with A-waves and frequencies of patients with A-waves were comparable between the ALS patients and normal controls. For the ulnar and tibial nerves, the frequencies of nerves with A-waves and frequencies of patients with A-waves were significantly increased in the ALS patients compared with those of the normal participants. Disease progression rate was slower in the ALS patients with A-waves (0.73 ± 0.99) than that in the ALS patients without A-waves (0.87 ± 0.55, P = 0.007). No correlations were found between the amplitudes of F-waves with A-waves and those of A-waves in the ulnar nerves (r = 0.423, P = 0.149). No correlations were found between the persistence of F-waves with A-waves and the persistence of A-waves in the ulnar nerves as well (r = 0.219, P = 0.473). The occurrence of A-waves may indicate dysfunction of lower motor neurons and possibly imply a relatively slower degenerative process.