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.
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.
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]:
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.
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 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].
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 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 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.
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.
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.
Your doctor will insert a needle into your muscle and record the electrical activity within the muscle.
MRI is used to look at the soft tissues and muscles. Patients with DMD may show damaged muscles on MRI.
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.
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.
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.
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.
