Episodic Muscle Disorders

PURPOSE OF REVIEW

This article reviews the episodic muscle disorders, including benign cramp-fasciculation syndrome, the periodic paralyses, and the nondystrophic myotonias. The core diagnostic criteria for a diagnosis of primary periodic paralysis, including clues to distinguish between the hypokalemic and hyperkalemic forms, and the distinctive elements that characterize Andersen-Tawil syndrome are discussed. Management of patients with these disorders is also discussed.

RECENT FINDINGS

Childhood presentations of periodic paralysis have recently been described, including atypical findings. Carbonic anhydrase inhibitors, such as dichlorphenamide, have recently been approved by the US Food and Drug Administration (FDA) for the treatment of both hypokalemic and hyperkalemic forms of periodic paralysis. Muscle MRI may be a useful outcome measure in pharmacologic trials in periodic paralysis. Genetic research continues to identify additional gene mutations responsible for periodic paralysis.

SUMMARY

This article will help neurologists diagnose and manage episodic muscle disorders and, in particular, the periodic paralyses and the nondystrophic myotonias.

Thyrotoxic periodic paralysis: a case report and literature review

We describe a 37-year-old man with a 4-month history of episodic muscular weakness, involving mainly lower-limbs. Hypokalemia was documented in one episode and managed with intravenous potassium chloride. Hyperthyroidism was diagnosed 4 months after onset of attacks because of mild symptoms. The patient was subsequently diagnosed as having thyrotoxic periodic paralysis associated with Graves' disease. Treatment with propranolol and methimazol was initiated and one year later he remains euthyroid and symptom free. Thyrotoxic periodic paralysis is a rare disorder, especially among Caucasians, but it should always be considered in patients with acute paralysis and hypokalemia, and thyroid function should be evaluated.

[Periodic paralysis: new pathophysiological aspects]

Periodic paralyses are neuromuscular disorders characterized by attacks of muscle weakness coinciding with changes in blood potassium levels. They are thus classified as hypokalaemic, normokalaemic or hyperkalaemic. Most forms are genetic, with autosomal dominant inheritance. These diseases are channelopathies, i.e. caused by mutations in ion channel genes. The culprit genes encode muscle sodium, calcium and potassium channels. Mutations in calcium or potassium channels cause periodic paralyses of the same type (hypokalaemic periodic paralysis or Andersen-Tawil Syndrome). In contrast, distinct mutations in the gene encoding the sodium channel can cause the entire range of periodic paralysis (hypokalaemic, normokalaemic or hyperkalaemic). The physiological consequences of mutations have been studied with patch-clamp techniques and electromyography. Generally speaking, mutations alter the excitability cycle of the muscle membrane, resulting in a loss of function (paralysis). Electromyographic studies have demonstrated a good correlation between symptoms and physiological parameters, giving rise to a classification that can help orient the molecular diagnosis. Work on the genetics and pathophysiology of periodic paralyses has helped to improve the diagnosis and management of these syndromes.

An unrecognized cause of paralysis in ED: thyrotoxic normokalemic periodic paralysis

Hypokalemic paralysis associated with hyperthyroidism (TPP) is a well-known acute electrolyte and muscle function disorder. Lesser known is normokalemic periodic paralysis associated with hyperthyroidism. We describe two cases of young men with acute muscular paralysis and bilateral impairment of sensation over the lower legs who had normal plasma potassium concentrations. They were initially misdiagnosed as having Guillain-Barré syndrome or hysterical paralysis. However, thyroid function tests showed elevated serum T(3) and T(4) and markedly depressed thyroid-stimulating hormone findings consistent with hyperthyroidism. Control of the hyperthyroidism completely abolished their periodic paralysis. Thyrotoxic normokalemic periodic paralysis (TNPP) should be kept in mind as a cause of acute muscle weakness to avoid missing a treatable and curable condition.

[HYPP: hyperkalemic periodic paralysis in the horse]

Hyperkalaemic periodic paralysis(HYPP) is characterized by intermittent episodes of muscular tremor, weakness, and collapse, and is probably caused by abnormal electrolyte transport in the muscle cell membrane. During an episode of HYPP, most animals are severely hyperkalaemic. HYPP is a hereditary disease and occurs only in American Quarter horses or crossbreds. Because these horses are now being imported into the Netherlands, HYPP should be included in the differential diagnosis of horses showing signs of muscle tremor, paresis, or paralysis. The present article reviews the literature on HYPP and describes a case showing typical signs of the disease.

Thyrotoxic periodic paralysis in a Jamaican male

Thyrotoxic periodic paralysis is a rare endocrine disorder most prevalent among individuals of Asian descent that presents as proximal muscle weakness, hypokalemia, and signs of hyperthyroidism. We present the case report of a patient with previously undiagnosed hyperthyroidism, protracted muscle weakness with transient exacerbations, and nocturnal onset of periodic paralysis affecting the upper and lower limbs.

Fibromyalgia in hyperkalemic periodic paralysis

A 43-year-old woman presented at the age of 38 with joint pains and muscle stiffness. Tender points were found fulfilling ACR criteria (1) for fibromyalgia. She had well developed muscles and decreasing muscle power since the age of 35. Muscle pains increased after exercise. Her 10-year-old son had similar symptoms and one paralytic attack. Muscle pain and fatigue increasing with age were found by history in three close relatives. Forearm cold water test produced myotonia in both mother and son. Electromyography was normal and muscle biopsy showed minor unspecific changes. Biochemical investigation of muscle mitochondrial function was normal. Peroral potassium load test produced complete muscle paralysis at a potassium serum level of 5.0 mmol/l. Autosomal dominant hyperkalemic periodic paralysis was diagnosed. Frequent carbohydrate enriched meals, peroral bendroflumethiazide and restriction to submaximal exercise improved muscle and joint pain. Salbutamol peroral spray relieved the periodic weakness.

[A case of potassium-sensitive periodic paralysis with cardiac dysrhythmia]

The authors reported a case of potassium-sensitive periodic paralysis with cardiac dysrhythmia. The patient was a 21-year-old male and had periodic paralysis and asymptomatic cardiac dysrhythmia since the age of 12. His attacks worsened in frequency and intensity which brought him to our hospital at the age of 21. Physical examination on admission revealed slight dysmorphic features such as hypoplastic mandible and high-arched palate. He had slight proximal muscle atrophy with no myotonia. Electrocardiogram showed multifocal ventricular arrhythmia. The serum potassium levels during his paralytic attacks were normal or slightly decreased (3.6-4.2 mEq/l). Both potassium and glucose tolerance tests provoked paralytic attacks. Glucose tolerance test also aggravated his cardiac dysrhythmia. Acetazoramide administration improved his paralytic attack. Potassium-sensitive periodic paralysis with cardiac dysrhythmia can not be defined by the classification of periodic paralysis based on the serum potassium concentration. Provocative tests should be done to make a definite diagnosis and treatment should be done taking into consideration both paralytic attack and cardiac dysrhythmia.

[Gamstorp's disease and pregnancy. A case report]

Gamstorp's disease or hyperkaliemic periodic paralysis is a rare pathology leading to spells of generalized hypotonia due to hyperkaliema. It is hard to say how far pregnancy affects the course of the disease and what is the impact of the disease on pregnancy. We report a case of Gamstorp's disease during pregnancy and we insist on the fact that because it can be crippling during its acute phases, close surveillance is needed during pregnancy. Screening for malignant hyperthermia should be carried out. During labour, kaliemia level should be monitored repeatedly and the expulsion phase kept as short as possible if necessary by forceps delivery.

[American Quarter Horses and HYPP]

Hyperkalaemic periodic paralysis is a genetic disease that affects the American Quarter Horse population and is caused by a mutation. As a result of this mutation in a gene which codes for the sodium channel in muscle cells, severe muscle weakness can appear. Reliable DNA-tests can establish whether a horse is homozygous negative, heterozygous, or homozygous positive for this mutation. Therapy and prevention are discussed.

Thyrotoxic hypokalemic periodic paralysis: report of four cases in black American males

Thyrotoxic periodic paralysis (TPP) is an unusual complication of a fairly common disease affecting mostly Asian males. In the United States, there have been several reports of TPP in different ethnic populations and it appears that the incidence is approximately one-tenth of that found in Asian countries. Only six reports of TPP in African-Americans could be found in the literature; however, we are reporting four cases diagnosed within a 13-year period at our institution. We conclude that TPP may occur more often in Blacks than previously suspected and should be considered when patients present with unexplained hypokalemia, muscular weakness and rhabdomyolysis. The epidemiology, clinical manifestations, pathophysiology, and treatment of TPP are reviewed.

Hyperthyroidism with gynaecomastia, galactorrhoea and periodic paralysis

A 32 year old male thyrotoxic presenting with gynaecomastia, galactorrhoea and later complicated with hypokalaemic periodic paralysis is presented. The gynaecomastia and galactorrhoea resolved with treatment. To the best of the author's knowledge this combination of association in one patient has not been reported previously.

Severe hypokalemia in thyrotoxic periodic paralysis

Thyrotoxic hypokalemic periodic paralysis is an uncommon but sometimes fatal disease in which early recognition and therapy may prevent untoward complications. The case of a 26-year-old Chinese man who presented to the emergency department with rapidly progressive profound weakness and severe hypokalemia (serum potassium, 1.2 mEq/L) is presented. The patient required endotracheal intubation, ventilatory assistance, and intravenous potassium administration. Emergency medical evaluation and management of this entity are discussed.