Muscular dystrophy and arthritis
Michael Horvat, Ronald V. Croce, Caterina Pesce, Ashley Fallaize in Developmental and Adapted Physical Education, 2019
Myotonic muscular dystrophy (Steinert’s disease) is the second most common adult form of muscular dystrophy. It is autosomal dominant and characterized by abnormalities in muscle contraction (Jones, 1985). Myotonia, the primary characteristic of this disease, is usually not clinically or electromyographically evident until 5 years of age, unless it is the congenital form that is diagnosed at birth and results in severe cognitive deficits (Sarnac, 1992). Myotonia is the delay or inability to relax muscles after repetitive discharge, or contraction, of a single muscle fiber after activation induced by the stretch reflex or electrical stimulation (Sarnac, 1992). Myotonia is commonly demonstrated in the hands and distal muscles. Speech is often affected because of involvement of the muscles of the face, tongue, and pharynx. Cardiac involvement is manifested by blocks in the Purkinje system, and arrhythmias instead of cardiomyopathy present in other dystrophic conditions (Sarnac, 1992). Facial features include masseter muscle atrophy and inability to close the lips. The eye muscles are weak, affecting the ability to close the eyes. Neck muscles atrophy and are weak mainly in flexion, causing some cervical lordosis. Weakness in the extremities is present in distal muscles, characterized by weak hand muscles and foot drop. As with other types of muscular dystrophy, learning difficulties may occur, and no specific medical treatment can counteract these symptoms.
Psychosocial Issues and Case Management in Myotonic Muscular Dystrophy
Leon I. Charash, Robert E. Lovelace, Claire F. Leach, Austin H. Kutscher, Rabbi Jacob Goldberg, David Price Roye, Jill C. Crabtree in Muscular Dystrophy and Other Neuromuscular Diseases: Psychosocial Issues, 2014
Myotonic muscular dystrophy (DM) is the most prevalent form of muscular dystrophy. Steinert (1909) described it as a slowly progressive disease that initially affects the distal musculature with weakness and atrophy. Facial muscles are also involved, causing the “myotonic facies,” a hatchet-like appearance, often in conjunction with alopecia. This disease can progress to involve the proximal muscles and may cause severe ambulation difficulties that require the patient to use a wheelchair for mobility. Clinically, myotonia is the difficulty of the muscle to relax. Myotonia is demonstrated as sustained deplorization (dive bomber effect) on electromyogram (EMG) (Davison 1961; Lipicky and Bryant 1973) and by percussion on clinical exam (Appel and Roses 1978; Harper 1979).
Diseases of Muscle and the Neuromuscular Junction
John W. Scadding, Nicholas A. Losseff in Clinical Neurology, 2011
Attacks of generalized weakness usually begin in childhood. The attacks most commonly start in the morning and last less than an hour. Serum potassium becomes elevated, usually to greater than 5 mmol/L. Recovery is often improved by exercise, although some mild weakness may continue for several days. Between attacks, the patient and serum potassium are normal. The frequency of attacks is very variable and they are generally not as severe as those with hypokalaemic periodic paralysis. They may be triggered by muscular exercise with subsequent rest, alcohol, fasting, pregnancy and potassium loading. Myotonia may be seen in some but not all patients. Some mutations in SCN4A are associated with the development of fixed weakness.
Ophthalmological Manifestations of Hereditary Myopathies
Published in Journal of Binocular Vision and Ocular Motility, 2022
Marta Saint-Gerons, Miguel Angel Rubio, Gemma Aznar, Ana Matheu
Myotonic syndromes are a group of very heterogeneous etiology disorders that are characterized by the presence of clinical or electrical myotonia. Myotonia is clinically defined as a difficulty of post-contraction muscle relaxation. In electromyography, the presence of high-frequency discharges, derived from excessive irritability of the muscular membrane is observed. Two groups can be differentiated: the first consisting of myotonic dystrophy and proximal myotonic myopathy, and the second, non-dystrophic myotonia. In contrast to myotonic dystrophy, in the non-dystrophic myotonia, there is no significant destruction of muscle tissue, most of them are caused by alterations of the genes that encode subunits of ion channels. This group includes periodic paralysis syndrome, paramyotonia congenita, and myotonia congenita in its dominant or recessive forms43 (Table 3).
Sodium Channel Myotonia and a Novel Gly701Asp Mutation in the SCN4A Gene: From an Ophthalmological Symptom to a Familial Disease
Published in Neuro-Ophthalmology, 2021
Filipa Sampaio, Sérgia Soares, Sara Pereira, José Alberto Lemos, Ágata Mota
The non-dystrophic myotonias are caused by dysfunction of key skeletal muscle ion channels. The worldwide prevalence of non-dystrophic myotonia has been estimated to be 1 in 100 000.1 The major clinical manifestation of the non-dystrophic myotonias is muscle stiffness and additional common symptoms include pain, weakness and fatigue.2,3 Myotonia can be demonstrated on examination as delayed muscle relaxation following muscle contraction. Non-dystrophic myotonias are classified as myotonia congenita, caused by mutations in the skeletal muscle chloride channel gene (CLCN1) and inherited in a dominant or in a recessive fashion; paramyotonia congenita and the sodium channel myotonias, characterised by allelic, autosomal dominant disorders caused by mutations in the skeletal muscle sodium channel gene (SCN4A); and hyperkalaemic periodic paralysis, also caused by mutations in SCN4A gene in which episodic paralysis is usually the dominant feature (Table 1).4
Mexiletine (NaMuscla) for the treatment of myotonia in non-dystrophic myotonic disorders
Published in Expert Opinion on Orphan Drugs, 2020
Karen J. Suetterlin, Dipa Raja Rayan, Emma Matthews, Michael G Hanna
Thus, treatment is often necessary for the symptoms of NDM. However, until recently there has been no licensed treatment for myotonia. The recommended therapeutic approach has been that patients with mild symptoms are encouraged to avoid triggers such as cold or strenuous exercise and make use of the warm-up phenomena with an emphasis on gentle warm-up and warm down prior to activity and avoidance of sudden movements whenever possible. When pharmacological intervention is required, the recommended first-line treatment for myotonia has been off-license use of mexiletine [16] (Box 1), or more recently, lamotrigine [17]. Recommended second-line treatments include other anticonvulsants or antiarrhythmics such as carbamazepine, phenytoin, and flecainide but these have varying efficacy [18,19].
Related Knowledge Centers
- Channelopathy
- Electromyography
- Myotonia Congenita
- Neuromuscular Junction
- Skeletal Muscle
- Ion Channel
- Paramyotonia Congenita
- Myotonic Dystrophy
- Brody Myopathy
- Ion Transporter