Myotonic disorders comprise both dystrophic myotonia and non-dystrophic myotonia. These conditions are caused by the mutation of specific genes which affect normal muscle function. The common feature that these conditions share is myotonia, during which muscles relax slowly and with difficulty after a voluntary contraction. This can cause stiffness, cramping, or an aching sensation in affected muscles, as well as muscle pain. Dystrophic myotonia is associated with muscle stiffness and systemic complications such as heart abnormalities which may be linked to sudden death, whereas non-dystrophic myotonia is mainly associated with muscle stiffness and muscle pain.
Mexiletine is under registration in Europe for the symptomatic treatment of myotonic disorders. It is administered as an oral capsule and it exerts its action by reducing the rate of contraction in the heart and other muscles. Currently it is used unlicensed in the UK, meaning that it is not currently approved but some healthcare providers consider it to be potentially beneficial based on research or professional experience. There are currently no licensed treatment options available to treat symptoms of myotonia, therefore, if licensed, mexiletine will offer access to an approved treatment option.
Tofacitinib works by blocking the action of enzymes known as Janus kinases. These enzymes play an important role in the inflammatory process. By blocking the enzymes’ action, tofacitinib helps reduce the inflammation and other symptoms of these diseases. Tofacitinib is an oral alternative to the available biological medicines for children with JIA, most of which are administered by injection. If licensed, tofacitinib may offer an additional treatment option for polyarticular JIA with the potential advantage of improving the quality of life of children due to its oral formulation.