Current concepts review: Low-vs high-tone neuromuscular spinal deformities: An evolving distinction with clinical implications.

Background: Neuromuscular scoliosis (NMS) was historically classified into two groups as neuropathic and myopathic, which offers limited benefit beyond describing the underlying pathology. More recently, NMS is being classified according to changes in muscle tone, which more accurately characterizes presenting features, and also helps emphasize the critical differences in management. Clinical Presentation: High-tone NMS, with cerebral palsy (CP) as a typical example, is characterized by spasticity, rigidity, and often reduced flexibility. Low-tone NMS, as in spinal muscular atrophy (SMA) and muscular dystrophy presents with hypotonia and truncal weakness, leading to more flexible, long curves often with significant kyphosis. High burden of medical comorbidities is common in both groups, while low-tone patients carry a higher risk of respiratory failure secondary to severe muscle weakness and cardiac involvement in myopathies and muscular dystrophies. Management: Successful management depends on careful evaluation of muscle tone, and tailoring the treatment accordingly. Multidisciplinary care is essential, and preoperatively all patients should be evaluated for possible respiratory problems and nutritional optimization. Muscular dystrophies and myopathic conditions require careful cardiac evaluation. Principles of surgical treatment may be similar for both low-tone and high-tone patients, but characteristics of the underlying disease can affect the details of treatment. Conclusion: Surgery can be performed safely and provide significant improvements in quality of life in NMS. Recent evidence suggests that surgery may also decrease mortality and help preserve pulmonary function. Distinguishing low-from high-tone NMS provides a clinically meaningful framework.