A new study using muscle ultrasound found that patients with amyotrophic lateral sclerosis and spinal and bulbar muscular atrophy may have shown widespread fasciculations, but with clear differences in distribution and intensity.
In the study, researchers included 24 men with spinal and bulbar muscular atrophy (SBMA) and 16 patients with amyotrophic lateral sclerosis (ALS). They examined 12 muscle groups using ultrasound—including the tongue, arms, trunk, and legs—to better understand fasciculation patterns in each disease, which can sometimes present with overlapping clinical features.
Fasciculations were observed in all patients in at least two muscles. In SBMA, they most frequently occurred in the tongue (100%), first dorsal interosseous (93%), and tibialis anterior (80%). In contrast, patients with ALS demonstrated more widespread fasciculations, particularly in proximal limb and trunk muscles.
When present, fasciculations were more intense in the patients with ALS. For instance, average fasciculation intensity in the biceps brachii was 2.5 in ALS compared with 1.4 in SBMA. Intensity was also higher in the triceps, rectus abdominis, and biceps femoris. Tongue fasciculation intensity was similar in both groups.
The researchers developed a modified ultrasound scoring system using six muscles: tongue, biceps brachii, triceps brachii, rectus abdominis, biceps femoris, and tibialis anterior. A score of 7.5 or higher distinguished ALS from SBMA with 93% sensitivity and 83% specificity.
"In clinical practice, the absence of tongue muscle fasciculations on ultrasound may serve as strong evidence for excluding SBMA from the diagnosis. However, SBMA and ALS can currently be differentiated through clinical history and findings, [electromyography] (EMG), and genetic testing. Therefore, ultrasound should not be considered a replacement for existing diagnostic methods but may serve as a complementary tool, particularly in cases where clinical and electrophysiologic findings are inconclusive," said lead study author Takeru Nara, of the Department of Rehabilitation Medicine at the Chiba University Hospital in Japan, and colleagues.
All of the patients with SBMA were male, with confirmed CAG repeat expansions in the androgen receptor gene. Their mean age was 58.6 years. The patients with ALS were older (mean age = 67.1 years) and had shorter disease duration (20.1 months vs 164.5 months in SBMA).
Ultrasound assessments were conducted by trained examiners using standardized protocols. Each muscle was observed in three regions for 30 seconds to detect fasciculations.
No statistically significant correlations were found between fasciculation characteristics and clinical measures such as disease duration or grip strength.
While ultrasound isn't a replacement for EMG or genetic testing, the researchers suggested it can serve as a useful noninvasive tool to help differentiate ALS from SBMA based on fasciculation profiles.
The authors reported no conflicts of interest.
Source: BMJ Neurology Open
