February 26, 2021

Distal Muscular Dystrophy: Symptoms, Diagnosis, and Management

Written by: Syed Naqvi, MBBS
Reviewed by: Mubashar Rehman, PHD

What is Distal Muscular Dystrophy?

Distal muscular dystrophy (DMD) is a distal disease that consists of a group of rare muscle diseases (i.e., myopathies). These diseases generally start from distal muscles (i.e., muscles of hands and feet) and then spread to the rest of the body. 


Causes:

DMD is a genetic disease and may be inherited in a dominant or a recessive pattern[1]. Our genes are programming codes that define each feature of our bodies, that is, eye color, hair pattern, skin complexion, etc. Each person has a pair of genes, one inherited from their father and one from their mother. If the disease manifests due to mutation in a single gene, it is said to be inherited in the dominant pattern. On the other hand, if the disease manifests only after both the genes of the pair are mutated, it is said to follow the recessive pattern. DMD is caused by mutation or lack of specific proteins that are required in making functional muscles.


Types:

Distal muscular dystrophy is classified into several types. They differ in their pattern of inheritance and the type of muscular protein affected. The general symptoms are more or less similar in various types. However, some symptoms are more predominant in one type than the other. Different types of DMD are given below[2]:

  1. Laing Distal Myopathy
  2. Tibial Muscular Dystrophy
  3. Miyoshi Myopathy
  4. Welander Distal Myopathy
  5. Nonaka myopathy
  6. Distal Myopathy with Vocal Cord and Pharyngeal Signs


Distal Muscular Dystrophy Symptoms in Adults

DMD have wide-ranging symptoms involving muscles of different types. Typically, skeletal muscles are involved. However, cardiac muscle and vocal cord involvement has also been seen. Most of the patients will present with symptoms in their adulthood if the inheritance pattern is dominant. Patients with recessive diseases usually start having symptoms during childhood. DMD predominantly causes distal muscle weakness. 


Distal Myopathy:

Patients with DMD may present initially with myopathy of distal muscles[3]. Muscular dystrophy of legs presents with foot drop (i.e., patients will not be able to move their feet upwards at the ankle joint) and writing difficulties due to involvement of muscles in the hands. Patients with a foot drop will have difficulty in walking since they would not be able to put heel-first while walking and would need to lift up their legs at knee joint. The resulting gait would look as if the patient were slapping the floor with their sole of the feet (ie, steppage gait).


Cardiomyopathy:

Cardiomyopathy is characterized by abnormal proteins in the heart muscles. It would lead to an inability of the heart to pump blood efficiently. Patients would have shortness of breath especially with physical exertion. Laing distal myopathy is associated with cardiomyopathy since it is caused by a mutation in the MYH7 gene that is responsible for encoding the beta-cardiac myosin protein[4].


Calves Pseudohypertrophy:

Miyoshi myopathy presents initially with degeneration of calf muscles and their replacement with fatty tissues. This replacement with fatty tissues makes the calves abnormally large. This is called pseudohypertrophy. Although the calves are enlarged, the patient would not be able to use the calf muscles as they are replaced by fatty tissues. Patients will have difficulty standing on tiptoes. Calves pseudohypertrophy may be seen in Miyoshi myopathy [5].


Dysphagia and Dysphonia:

Dysphagia refers to difficulty with speaking, while dysphonia refers to difficulty in speaking. Patients with distal myopathy with vocal cord and pharyngeal signs usually present with the involvement of vocal cords and swallowing muscles of the pharynx[6]. The pharynx is a part behind the tongue and above the esophagus. It is involved in speaking as well as swallowing. Hence, myopathy of pharyngeal muscles leads to dysphagia and dysphonia.


Proximal Myopathy:

Proximal myopathy refers to the involvement of muscles of the hip and shoulder. These muscles are not initially involved in distal muscular dystrophy. The name itself tells that the predominantly involved muscles are the distal muscles of hands and feet. However, as the disease progresses, patients will also have the involvement of proximal muscles. This leads to permanent disability. A good mobility device would help in carrying out daily activities at a limited functional status.


Diagnosis of Distal Muscular Dystrophy

Apart from assessing the clinical features, your doctor would ask you about personal and family history. Your doctor will also assess your muscles’ functional status by asking you to perform several muscle movements to assess which muscles are involved. Apart from clinical and physical examination, your doctor might also order several investigation tests to confirm the diagnosis.


Blood Tests

Your doctor might order a blood test to check the level of creatine kinase in the blood. Creatine kinase is normally found in the muscles. When muscles are damaged, creatine kinase is spilled into the blood, therefore its level within the blood starts to rise.


Electromyography:

Your doctor will insert a needle into your muscle and record the electrical activity within the muscle.


MRI:

MRI is used to look at the soft tissues and muscles. Patients with DMD may show damaged muscles on MRI.


Biopsy:

A biopsy involves cutting out a small piece of the muscle and studying it under microscopy. A biopsy of the muscle affected by DMD may show damaged cells, increased connective tissue, and fat.


Genetic Studies:

Your doctor will most likely order a genetic test to confirm the diagnosis. A genetic test would show which genes are mutated and will confirm the diagnosis even if the patient is asymptomatic or mildly symptomatic.


Management of Distal Muscular Dystrophy

DMD is a rare disease and no cure has been discovered yet. The treatment is focused on the management of symptoms. Treatment options may include physical therapy and the use of assisting devices such as braces or wheelchairs for locomotion. Due to immobility, a patient may have the stiffness of joints leading to deformity and pain. This can be prevented with regular range of motion exercises. 


Summary

Distal muscular dystrophy is a group of rare and debilitating diseases. A person may have an increased risk of having this disease if they have other family members with this disease. Patients usually present with myopathy of distal muscles, cardiomyopathy, difficulty in swallowing, and difficulty in speaking. There is no cure for distal muscular dystrophy but physical and occupational therapies may be helpful to manage the symptoms.


References

  1. Lovering RM, Porter NC, Bloch RJ. The muscular dystrophies: from genes to therapies. Phys Ther. 2005;85(12):1372-1388.
  2. Diseases - Distal Myopathies - Types Of Overview | Muscular Dystrophy Association. Muscular Dystrophy Association. https://www.mda.org/disease/distal-myopathies/types. Published 2021. Accessed January 30, 2021.
  3. Udd B. Distal muscular dystrophies. Handb Clin Neurol. 2011;101:239-62. doi: 10.1016/B978-0-08-045031-5.00016-5. PMID: 21496636.
  4. Lamont P, Laing NG. Laing Distal Myopathy. 2006 Oct 17 [Updated 2015 Mar 12]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2021. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1433/
  5. Harris E, Bladen CL, Mayhew A, et al. The Clinical Outcome Study for dysferlinopathy: An international multicenter study. Neurol Genet. 2016;2(4):e89. Published 2016 Aug 4. doi:10.1212/NXG.0000000000000089
  6. Feit H, Silbergleit A, Schneider LB, Gutierrez JA, Fitoussi RP, Réyès C, Rouleau GA, Brais B, Jackson CE, Beckmann JS, Seboun E. Vocal cord and pharyngeal weakness with autosomal dominant distal myopathy: clinical description and gene localization to 5q31. Am J Hum Genet. 1998 Dec;63(6):1732-42. doi: 10.1086/302166. PMID: 9837826; PMCID: PMC1377645.
  7. Muscular Dystrophy. https://www.nhs.uk/conditions/muscular-dystrophy/types/
Article written by Syed Naqvi, MBBS
Dr Syed Naqvi is a graduate of King Edward Medical University which is one of the top medical schools in his country. He has a 10-year editorial experience working on different projects. He has spent countless hours in pursuing his lifelong dream as a doctor. Ever since clearing his United States Medical Licensing Exams, he has been pursuing different aspects of medical education to broaden his scope. His interests lie in medical education, philosophy, and writing. He likes to write books for personal use and recently finished a 3000-page medical book. He likes to spend his free time reading philosophy, psychology, and medical books.

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