In persons with paramyotonia congenita, symptoms typically appear early in life, anywhere from infancy to adolescence. Patients complain of an inability to relax muscles and weakening that worsens with repeated activity or prolonged exercise [1]. This is exactly the difference between paramyotonia and classic myotonia in which symptoms are alleviated by physical activity. Symptoms last from minutes to days. The most commonly affected muscles are those in the face and upper extremities [2].

Patients may report worsened symptoms during activities involving cold temperatures such as shoveling snow or while handling frozen foods. Women may experience exacerbation of symptoms during menstruation or pregnancy [3]. Parents may state that their infant's eyes appear to "stick" or the infant has difficulty opening his/her eyes following crying spell [4].

• Camping

  Hua Gu, Yan-Jia Fang, Dong-Dong Liu, Ping Chen, Yan-Ai Mei and Steven Barnes, cAMP/PKA Pathways and S56 Phosphorylation Are Involved in AA/PGE2-Induced Increases in rNaV1.4 Current, PLOS ONE, 10, 10, (e0140715), (2015). [doi.org]

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• Difficulty Walking

  walking Vasculitis Pain, weakness, numbness of arms and legs Metabolic Diseases of Muscle Symptoms Acid maltase deficiency Muscle weakness, dark-colored urine myoglobinuria, elevated CK or CPK, muscle fatigue, muscle cramps Carnitine deficiency Carnitine [nationwidechildrens.org]

• Dyspnea

  […] limbs and myotonia 5 Myotonic dystrophy Systemic features Ocular : Cataract, ptosis, retinal degeneration Cardiac:Conduction disease, arryhtmias,cardiomyopathy Gastrointestinal: Dysphagia, colonic dysmotility, megacolon Diaphragmatic weakness can cause dyspnea [slideplayer.com]

  However, when the patient was extubated following surgery, she exhibited acute dyspnea in the operating room and was immediately re-intubated and transferred to the intensive care unit. [link.springer.com]

• Myopathy

  Paramyotonia congenita (OMIM 168300) is a non-dystrophic myopathy caused by mutations in the SCN4A gene that sometimes can be confused with myotonia congenita. [ncbi.nlm.nih.gov]

  Hanna, Periodic paralysis, Myopathies, 10.1016/S0072-9752(07)86004-0, (77-106), (2007). Frank Lehmann‐Horn and Karin Jurkat‐Rott, Myotonic disorders, Myopathies, 10.1016/S0072-9752(07)86003-9, (61-76), (2007). J.G. McGivern and J.F. [doi.org]

• Myalgia

  PARAMYOTONIA CONGENITA WITHOUT COLD PARALYSIS, INCLUDED Classification genetic, neurological Phenotypes Autosomal dominant inheritance ; Feeding difficulties ; Handgrip myotonia ; Infantile onset ; Inspiratory stridor ; Muscle stiffness ; Muscle weakness ; Myalgia [mousephenotype.org]

  […] dystrophy type I (DM1, Curschmann-Steinert disease) Myotonic dystrophy type II (DM2, proximal myotonic myopathy) Clinical features Myotonia: delayed muscle relaxation following normal muscle contraction Skeletal muscle weakness(due to muscle atrophy) Myalgia [amboss.com]

  Genes related to Paramyotonia Congenita Of Von Eulenburg SCN4A View recommended genes panels Clinical Features Top most frequent phenotypes and symptoms related to Paramyotonia Congenita Of Von Eulenburg Feeding difficulties Dysphagia Neonatal hypotonia Myalgia [mendelian.co]

  Early reports suggested that patients with myoadenylate deaminase deficiency had various forms of myalgia, and exercise intolerance. [scielo.br]

Evaluation for paramyotonia congenita includes a medical history of the patient as well as his/her family, physical examination, and neuromuscular testing. Myotonia will worsen with repeated or prolonged movement and then ultimately resolve after a period of minutes to days [1]. Symptoms are worsened by exposure to cold temperatures [2]. Patients may provide a history of anesthetic complications [5]. The patient's family history will often reveal similar symptoms or "cold intolerance" in relatives. Hypertrophy of affected muscles may be present in adults.

Tests commonly used to establish a diagnosis of paramyotonia congenita include:

• Genetic analysis - Mutations of the SCN4A gene can be confirmed by genetic testing. A mutation of this gene confirms the diagnosis of paramyotonia congenita [6].
• Electromyography (EMG) - EMG findings facilitate differentiation between paramyotonia congenita and myotonia congenita [7] [8]. In patients with paramyotonia congenita, EMG will show diffuse myotonic discharges, which are more pronounced with cooling of the affected muscles, as well as a total absence of muscle contractures with progressive cooling [9].
• Muscle cooling - Lowering a temperature of affected muscles to 20-25°C induces muscle paralysis and stiffness, which persists even after rewarming. Exercise while the muscle is cooled results in exacerbation of muscle weakness and decreased compound muscle action potentials [10].
• Exercise test - Exercise test is performed to confirm periodic paralysis. A positive test is characterized by two key findings in affected muscles: compound muscle action potentials are decreased and weakening of the muscle with exercise [11].
• Muscle biopsy - A muscle biopsy showing vacuoles confirms the presence of non-specific myopathy [12] [6]; however, it does not confirm a diagnosis of paramyotonia congenita.

Laboratory tests do not confirm the diagnosis of paramyotonia congenita, but may help rule out other conditions. Patients with paramyotonia congenita may have a normal or slightly elevated creatine kinase level and/or normal or increased potassium level [13] [14] [15].

Thiazide treatment in these two patients was ineffective. All seven patients responded well to tocainide. Treatment response and side effects were dose-dependent. [ncbi.nlm.nih.gov]

Pushpa Narayanaswami, Treatment and Management of Disorders of Neuromuscular Hyperexcitability, Neuromuscular Disorders: Treatment and Management, 10.1016/B978-1-4377-0372-6.00017-7, (285-306), (2011). Satish V. Khadilkar, R.K. Singh, K.A. [doi.org]

There is no cure for this disease and treatment usually includes avoiding activities that lead to symptoms. If your child has been diagnosed with paramyotonia congenita, talk to their doctor about all treatment options. [diseaseinfosearch.org]

Prognosis The 'prognosis' of Paramyotonia congenita usually refers to the likely outcome of Paramyotonia congenita. [checkorphan.org]

Prognosis Paramyotonia congenita has an excellent prognosis. [encyclopedia.com]

Paramyotonia congenita has an excellent prognosis. [medigoo.com]

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Because hyperkalemic periodic paralysis can occur in some families with PMC, it has been suggested that the 2 diseases share a common etiologic basis. [doi.org]

The overlap between various syndromes and etiologies can be confusing. [now.aapmr.org]

Many etiologies result in myotonia, including dystrophic and non-dystrophic myotonias. [statpearls.com]

ETIOLOGY:- The presentation of myotonia can result from a diverse array of etiologies. [samarpanphysioclinic.com]

PMC has not previously been described in Denmark and an epidemiological description of the family is given. [ncbi.nlm.nih.gov]

Epidemiology Paramyotonia congenita is considered an extremely rare disorder, though little epidemiological work has been done. Prevalence is generally higher in European derived populations and lower among Asians. [muscle-diseas.blogspot.com]

Epidemiological estimates have been provided for the German population. [ipfs.io]

Epidemiological estimates have been provided for the German population. Here, it was estimated that the prevalence of PC is between 1:350,000 (0.00028%) and 1:180,000 (0.00056%). [medigoo.com]

Ruben, Physiology and Pathophysiology of Sodium Channel Inactivation, Na Channels from Phyla to Function, 10.1016/bs.ctm.2016.04.001, (479-509), (2016). W. David Arnold, Daniel H. [doi.org]

Emphasis has been placed on the diagnosis and management of these disorders rather than on their pathophysiology. [books.google.com]

This pathophysiological mechanism can lead to an initial burst of myotonia discharges and result in the symptom of stiffness. [tandfonline.com]

Pathophysiologic and anesthetic considerations for patients with myotonia congenita or periodic paralyses. Paediatr Anaesth 2013 ; 23: 824 – 833. Google Scholar Medline [journals.sagepub.com]

Tocainide prevented myotonia and weakness induced by cooling, but failed to prevent hyperkalemic weakness. Hydrochlorothiazide prevented hyperkalemic weakness, but did not influence symptoms evoked by cooling. [ncbi.nlm.nih.gov]

Avoidance of myotonia triggering events is also an effective method of mytonia prevention. Resources - Paramyotonia congenita Not supplied. [checkorphan.org]

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15. Matsumura T Saito T, Yonemoto N, et al. Renal dysfunction can be a common complication in patients with myotonic dystrophy. Neurol Sci. 2016;368:266-271.