Myotonic Dystrophy

Original Editor - Kehinde Fatola
Top Contributors - Ananya Bunglae Sudindar, Kehinde Fatola and Kim Jackson

Introduction

Myotonic dystrophy also known as dystrophia myotonica or myotonia atrophica, is an autosomal dominant hereditary multisystemic disease that is chronic, slow-progressing, and very variable. It's an illness that runs in families. A form of muscular dystrophy in which cataracts, heart conduction abnormalities, endocrine alterations, and myotonia are all symptoms.

Myotonic dystrophy (DM) is an hereditary, affecting males and females approximately equally. About 30,000 people in the United States are affected. Symptoms may surface at any time between infancy to adulthood. DM causes general weakness, usually beginning in the muscles of the hands, feet, neck, or face. It progresses gradually to involve other muscle groups, including the heart. DM affects a wide range of other organ systems as well. A severe form of DM, congenital myotonic dystrophy, may be seen in babies of mothers who have DM. Congenital Myotonic Dystrophy can also be inherited through the gene of the father, although it was reported to be relatively rare. Many professionals however believe it is only via the maternal gene, however this has been disproved in recently. The January 2022 orphanet Report Series put the prevalence at 8.78 in 100000 persons.

Types

There are two main types of myotonic dystrophy.

Type 1 (DM1), also known as Steinert disease, is due to mutations (expansion) on the cytosine-thymine-guanine (CTG) triplet repeat in the DMPK gene on the long arm of Chromosome 19 and has a severe congenital form and a less-severe childhood-onset form as well as an adult-onset form [[2]] . This disease in more common in the facial muscles, levator palpebrae superioris, temporalis, sternocleidomastoids, distal muscles of the forearm, hand intrinsic muscles, and ankle dorsiflexors.

Type 2 (DM2), also known as proximal myotonic myopathy (PROMM), is rarer and generally manifests with milder signs and symptoms than DM1 The specific defect is a repeat of the cytosine-cytosine-thymine-guanosine (CCTG) tetranucleotide in the ZNF9 gene on Chromosome 3.

Clinical Presentation

DM usually have manifestations on the muscular, respiratory, cardiac, nervous, gastrointestinal and endocrine systems. However, clinical presentation varies considerably as the DM type and DM2 is generally milder than DM1. Some of the possible symptoms include;

• Difficulties in cognition and communication.
• Somnolence
• Apathy
• Deficit in executive functions (organisation and concentration)
• Depression
• Fatigue.
• Weakness of facial muscles (masseter and temporalis), neck muscles (sternocleidomastoid), long finger flexors of the hand and distal ankle muscles in DM1. In DM2, the muscular involvement is predominantly proximal (trunk, shoulders and pelvis) and also slowly progressive, beginning in the ‘mid-adult’ life.
• Coordination and balance impairment
• Cardiac arrhythmia
• Heart conduction abnormalities
• Dysphagia
• Heartburn
  

Management / Interventions

Like most other dystrophies, there's no known cure for MD and thus, management is generally symptomatic. Physiotherapy has been indicated to maximize range of motion and minimize muscular imbalances, avoid and minimize disuse atrophy, maximize functional abilities, conserve energy and prevent secondary injuries. Some of which are;

• Range of motion / stretching exercises
• Aerobic exercise
• Resistive exercises
• Balance training
• Orthosis may be recommended if there's an indication due to weak muscles

Differential Diagnosis

• Duchennes Muscular Dystropy
• Becker Muscular Dystropy
• Limb-girdle Muscular Dystropy
• Facioscapulohumeral muscular dystrophy
• Emery Dreifuss Muscular Dystropy
• Rigid spine syndrome
• Myopathies
• Myasthenia gravis
• Spinal muscular atrophy