Thomsen ‘s Myotonia
Thomsen’s myotonia (Leiden-Thomsen) is a genetic disease that is characterized by a lesion of the striated musculature, expressed in prolonged relaxation of the muscles after their contraction. Tonic muscle spasms begin immediately after active activity, lead to impaired motor skills.
The content of the article:
Etiology and pathogenesis of Thomsen’s myotonia
Symptoms of Thomsen’s myotonia
Diagnosis of Thomsen’s myotonia
Treatment of Thomsen’s myotonia
Prognosis and prevention
Thomsen ‘s Myotonia
The disease is inherited by autosomal dominant type and is quite rare: according to statistics, Thomsen’s myotonia affects 7 people per 1 million population. The first signs of myotonia appear at the age of 8-20 years and accompany the patient all his life. According to the results of the study of the clinic of nervous diseases I MMI, men are more likely to suffer from Thomsen myotonia. Out of 63 patients, 51 cases were recorded among males and 12 among females.
Etiology and pathogenesis of Thomsen’s myotonia
The hereditary disease is caused by a mutation of the CLCN1 gene. In etiopathogenesis, there are violations of myoneural conduction and pathology of intracellular membranes caused by a decrease in the permeability of the plasmolemma for chlorine ions into muscle fibers. The defect provokes an ionic imbalance: chlorine ions accumulate on the surface of the microfibrill without penetrating inside, which leads to bioelectric instability in the muscle membrane.
In the muscles of patients with Thomsen’s myotonia, the level of acetylcholine is increased, and in the cerebrospinal fluid and blood, there is a decrease in the activity of an enzyme involved in the regulation of excitability and contractility of muscle fibers.
Pathomorphology does not detect changes in muscle fibers inherent only in this disease. The tissue defect is typical for all kinds of myotonia. Light microscopy reveals hypertrophy of individual muscle fibers. Histochemistry determines the reduction of type II muscle tissue. Electron microscopy reveals moderate hypertrophy of the sarcoplasmic reticulum of muscle cells, an increase in the size of mitochondria, and an expansion of the telophragm of striated muscles.
Symptoms of Thomsen’s myotonia
Thomsen’s myotonia is a genetic disease, but external clinical signs are not detected immediately after birth. In most cases, the first symptoms are indicated in childhood (5-8 years) and adolescence (up to 20 years).
A feature of the clinical picture is a myotonic phenomenon characterized by:
hypotension of the muscles at rest;
hypertonicity, spasm of muscle fibers at the moment of volitional efforts;
prolonged muscle relaxation after the start of active movement.
Depending on the affected area, myotonic attacks can cover the legs, arms, neck muscles, shoulders, and face. As a result, muscle spasms are observed when you want to spread your fingers, clenched into a fist, at the moment of starting walking, when closing your jaws, closing your eyes, etc.
If Thomsen’s myotonia manifests at an early age, signs of muscle weakness are determined by the difficulty of the child’s physical development. The baby does not sit, does not get up, does not walk in due time, his body becomes uncontrollable.
At a later age, myotonic attacks of skeletal muscles are manifested when walking, the desire to stand up, to keep balance, that is, with any arbitrary movement. The patient, making the first motor act, feels a sharp muscle spasm and is immobilized. Wanting to get up, a person suffering from this disease necessarily relies on something. The first step when moving is given with great difficulty, sometimes tonic spasms are so strong that the patient falls. Squeezing the fingers of the hand into a fist, it is impossible to unclench them for 10 seconds or more, even if maximum effort is applied. Subsequent movements are made easier, spasms stop.
In the process of active activity, the affected muscles adapt to movement and the spasms disappear altogether. However, even after a short rest, muscle hypertonicity manifests itself with the same force.
In adulthood, a patient diagnosed with Thomsen’s myotonia may look like an athlete if the disease affects the muscles of the limbs and trunk. Due to constant overexertion, muscle mass is growing, the muscles are hypertrophied and look large, inflated.
The patient’s muscles react with strong excitement even with weak external stimuli. So, a light blow to the affected muscles can lead to their hypertonicity. At the place of touch, a tense muscle roller appears, which takes time to relax.
Myotonic attack is most often observed in two cases: in the initial phase of voluntary movement requiring the participation of diseased muscles and when exposed to cold. However, there are other provoking factors: prolonged stay in a static position, a sharp loud sound, an emotional outburst.
Diagnosis of Thomsen’s myotonia
The clinical picture gives every reason to determine the diagnosis by external signs. Careful collection of family history and features of clinical manifestations plays an important role.
At the initial appointment, the specialist uses a neurological hammer. By tapping lightly on the problem muscle area, the neurologist determines the ability of the muscles to contract and records the relaxation time after the impact. The formation of a roller at the point of contact reveals a myotonic symptom.
In confirmation of myotonia, the patient is offered to clench his fingers into a fist several times and unclench them. If the first movements are difficult, and then motor skills are normalized, then we can talk about the presence of tonic spasms. In some patients, there is a myotonic reaction of the pupils with convergence of the eyes.
The combination of neurological symptoms reveals a decrease in the tone of muscle tissue at rest and myotonic signs of tendon reflexes.
The tonic symptom complex is observed not only in Thomsen’s myotonia, but also in Eulenburg’s paramyotonia, Becker’s myotonia, Steiner’s myotonia, as well as in other neuromuscular and endocrine disorders. In this regard, the differentiation of the diagnosis and the designation of a certain type of myotonia is a great difficulty in diagnosis.
Differential diagnosis includes invasive and laboratory tests:
Muscle biopsy, which allows to identify histological changes in fibers that cause dysfunction of muscle cells;
Biochemical blood analysis. There are no specific biochemical markers for this disease. The study is conducted to determine the level of creatine phosphokinase activity in blood serum.
DNA test. One of the most informative tests to determine the mutation of the CLCN1 gene. The analysis is carried out in order to confirm the clinical diagnosis.
Electromyography (EMG). Invasive examination is carried out using a needle electrode. The instrument is inserted into the relaxed muscle, determining myotonic discharges and registering the potentials of motor units. Muscles are stimulated by an electrode and tapping, which causes their contractions. With repeated stimulation, the strength of myotonic spasms decreases.
Electroneurography (ENMG). The instrumental technique is carried out in order to diagnose the functional state of muscle tissue and their ability to contract when stimulated by an electric pulse. E N M G involves the use of surface (cutaneous) and intramuscular (needle) electrodes. Graphic registration of motor unit potentials is carried out using needle electrodes. The induced myotonic discharge is recorded through cutaneous electrodes displaying the total activity of the muscle.
Treatment of Thomsen’s myotonia
It is impossible to count on a complete cure. The main goal of drug and physiological therapy will be to relieve symptoms and achieve stable remission. For this purpose , the patient is prescribed:
Mexiletin is a sodium channel blocker that significantly reduces muscle hypertonia;
Diacarb — improves membrane permeability;
Quinine — reduces the excitability of muscles, increases the refractory period;
Diphenin is an effective anticonvulsant;
Diuretics — maintain ionic balance, maintaining magnesium levels and reducing potassium.
Long-term use of medications has negative aspects: all medications have a large range of side effects.
Non-drug therapy helps to improve metabolic processes in muscle tissue, reduce its tonic spasm:
Physical therapy;
Electrophoresis;
Acupuncture;
Therapeutic swimming.
Prognosis and prevention
The prognosis for life with Thomsen’s myotonia is favorable. However, it is impossible to get rid of myotonic attacks forever. But by taking a number of preventive measures, the patient is able to alleviate his condition and live a full life.
An important point is the determination of factors provoking myotonic seizures. Mainly it is impossible to overcool, it is necessary to avoid stressful situations, intense physical exertion, sudden movements, prolonged stay in one position, emotional shocks.
