Myotonic Dystrophy

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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 (eye, heart, brain, endocrine, gastrointestinal tract, uterus, skin) disease that is chronic, slow-progressing, and very variable. They present with the core features of myotonia, muscle weakness, and early onset cataracts.

Myotonic dystrophy (DM) is hereditary, affecting males and females almost equally and caused due to expansions of repetitive DNA sequences, known as trinucleotide repeats. 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 and it progresses gradually to involve other muscle groups, including the heart and 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.

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. 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 affectation is essentially multisystemic, impacting most physiologic functions in the body of patients. Clinical presentation differs per DM type but type 2 is generally less severe than type 1. Some of the possible symptoms include;

• Communication and intellectual difficulties
• Somnolence
• Apathy
• Deficit in executive functions
• Depression
• Fatigue.
• Weakness of muscles of the face and neck muscles as well as the flexors of the hand and distal ankle muscles in type 1.
• Weakness of the trunk, shoulders and pelvic muscles in type 2.
• Coordination and balance impairment
• Disruption to the electrical functions of the heart
  

Management / Interventions

Like most other dystrophies, there's no known cure for MD and thus, management is generally symptomatic. Physiotherapy has been indicated to improve ROM, prevent disuse atrophy, conserving energy, avoiding re-injury, and enhancing functional abilities while decreasing disability. 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