Skeletal muscle MRI differentiates SBMA and ALS and correlates with disease severity

Abstract

Objective: To investigate the use of muscle MRI for the differential diagnosis and as a disease progression biomarker for two major forms of motor neuron disorders, spinal bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS). Methods: We applied quantitative 3-point Dixon and semi-quantitative T1-weighted and STIR imaging to bulbar and lower limb muscles and performed clinical and functional assessments in ALS (n=21) and SBMA (n=21) patients, alongside healthy controls (n=16). Acquired images were analyzed for the presence of fat infiltration or edema as well as specific patterns of muscle involvement. Quantitative MRI measurements were correlated with clinical parameters of disease severity in ALS and SBMA. Results: Quantitative imaging revealed significant fat infiltration in bulbar (p<0.001) and limb muscles in SBMA compared to controls (thigh: p<0.001; calf: p=0.001), identifying a characteristic pattern of muscle involvement. In ALS, semi-quantitative STIR imaging detected marked hyperintensities in lower limb muscles, distinguishing ALS from SBMA and controls. Lastly, MRI measurements correlated significantly with clinical scales of disease severity in both ALS and SBMA. Conclusions: Our findings show that muscle MRI differentiates between SBMA and ALS and correlates with disease severity, supporting its use as a diagnostic tool and biomarker for disease progression. This highlights the clinical utility of muscle MRI in motor neuron disorders and contributes to establish objective outcome measures, which is crucial for the development of new drugs.

SOD1 mutations in adult‐onset distal spinal muscular atrophy

“…They should be considered pseudomyopathic changes, as previously described in the literature [3][4][5][6]. On the other hand, the fatty replacement observed in muscle magnetic resonance imaging (MRI) is compatible with slowly progressive denervation processes [7]. Clinical and electrophysiological analyses in both patients are consistent with a motor neuron disorder.…”

Phenotypic correlations in a large single‐center cohort of patients with BSCL2 nerve disorders: a clinical, neurophysiological and muscle magnetic resonance imaging study

“…As mentioned earlier, BSCL2 mutations may even present as an ALS‐like phenotype [5]. There is no specific pattern of fat replacement in ALS, but marked STIR changes from rapid denervation have been reported [40]. Although no ALS‐like phenotype was observed in our series, the predominantly distal involvement on MRI, notably tibialis anterior and soleus versus peroneal in ALS, and the more isolated STIR hyperintensities could help differentiate ambiguous cases.…”

MRI in Neuromuscular Diseases: An Emerging Diagnostic Tool and Biomarker for Prognosis and Efficacy

“…Although the fat replacement in muscular dystrophies typically affects specific muscles, whereas others are unaffected, muscle involvement is more diffuse and mottled in motor neuron diseases 29–31 . In spinal and bulbar muscular atrophy (SBMA), a pattern of progressive, diffuse, and mottled fat replacement of semitendinosus, semimembranosus, biceps femoris longus, triceps surae and spared sartorius, gracilis, biceps femoris brevis, and tibialis anterior has been found 29 .…”

“…In spinal muscular atrophy type III (SMAIII), the quadriceps femoris and iliopsoas are severely affected muscles, whereas gracilis and sartorius are spared. In amyotrophic lateral sclerosis (ALS), STIR hyperintensities indicating muscle edema, likely related to cell loss, are common and are followed by atrophy of muscle and mottled fat replacement of lateral calf muscles 31 . Fat replacement of the psoas muscles are unusual for muscle diseases.…”