Ultrasound assessment of muscle thickness and grip strength in neuromuscular disorders: the role of Vitamin D

Introduction: This retrospective cross-sectional study aimed to investigate the association between serum vitamin D levels and upper and lower extremity muscle thickness and muscle mass in patients with neuromuscular diseases (NMDs), as well as their relationship with nutritional status, handgrip strength, and fatigue.Methods: This retrospective cross-sectional study included 51 patients with a confirmed diagnosis of NMD for at least one year who were hospitalized for neuromuscular rehabilitation between January 2016 and January 2020. Demographic characteristics and laboratory parameters were obtained from medical records. Nutritional status was assessed using the Subjective Global Assessment, muscle strength using a Jamar dynamometer, and fatigue using the Fatigue Severity Scale. Muscle thickness was evaluated by ultrasonography of selected upper and lower extremity muscles on the dominant side.Results: The median serum vitamin D level was 19.82 ng/mL (9.01–39.82), and 62.7% of patients had normal nutritional status. No significant differences were observed among NMD subgroups regarding assessment parameters (p>0.05). Serum vitamin D levels were positively correlated with handgrip strength (r=0.651, p=0.001) and forearm flexor muscle thickness (r=0.693, p=0.001). Regression analysis demonstrated that handgrip strength and forearm flexor muscle thickness were independently associated with serum vitamin D levels. A one-unit increase in handgrip strength was associated with a 0.625-unit increase in serum vitamin D level, while a one-unit increase in forearm flexor muscle thickness was associated with a 1.459-unit increase in serum vitamin D level.Conclusion: In this inpatient NMD cohort, serum 25(OH)D levels were positively associated with handgrip strength and forearm flexor muscle thickness, while no clear associations were observed in other assessed muscle groups. Although causality cannot be inferred from this cross-sectional design, these findings suggest that vitamin D status may be linked to peripheral muscle function and morphology and should be considered when interpreting muscle-related outcomes in neuromuscular rehabilitation settings. Prospective, disease-specific studies with appropriate control groups are warranted.