Improving The Management of Non-dystrophic Myotonia to Benefit Care Delivery and Improve Patient Outcomes

Non-dystrophic myotonias (NDM) are rare muscle disorders caused by mutations in skeletal voltage-gated muscle channels leading to delayed muscle relaxation after voluntary contraction. They are subdivided into sodium channelopathies, when the mutation is in the SCN4A gene, and chloride channelopathies, when the mutation is in the CLCN1 gene. Symptoms, which may differ according to subtype, exacerbating factors, and over disease course, can include muscle stiffness, pain, fatigue, muscle hypertrophy, myalgia, and weakness. The severity of NDM symptoms varies widely, from being barely noticeable to causing considerable disability that impacts health-related quality of life. People with NDM may remain undiagnosed for several years, potentially due to a lack of awareness of NDM among many healthcare professionals. The symptomatic treatment for NDM predominantly involves sodium channel blockers, such as mexiletine. Randomised, placebo-controlled trials have shown mexiletine can reduce muscle stiffness and pain, and improve health-related quality of life. Patient and clinician surveys, as well as national guidelines, place this medication as one of the first choices for pharmaceutical treatment of myotonia. Other choices include lamotrigine, carbamazepine, acetazolamide, ranolazine, and flecainide, though clinical evidence is limited, and all are used on an off-label basis. Herein, the challenges in recognising and treating myotonia symptoms in people with NDM are reviewed, along with strategies to increase awareness of the disease and its potential treatment.