What Is Distal Muscular Dystrophy?

Distal muscular dystrophy (DD), also called distal myopathy, is not one disorder, but a group of genetic disorders under the larger umbrella of muscular dystrophy. DD is marked by progressive weakness and/or wasting of the voluntary distal muscles.

These are the muscles farthest from the center of the body, like hands and feet, and parts of the arms and legs. Although the age of onset can be at any time, most often it develops in later life and progresses slowly.

This article will provide an overview of distal muscular dystrophy, including the different types of DD, the causes, symptoms, and diagnosis and treatment options.

Types of Distal Myopathies

While DD is a type of distal myopathy, there are also several subtypes of DD. They can vary widely in severity, symptoms, and progression. Subtypes of DD can include:

• Distal myopathy with vocal cord and pharyngeal weakness: Symptoms usually start between ages 35 and 60 with weakness in the hands, legs, and voice, as well as difficulty swallowing.
• Finnish (tibial) distal myopathy: Weakness usually starts after age 40 in the lower extremities, especially in the muscles above the tibia, the larger long bone of the leg.
• Gowers-Laing distal myopathy: The onset can be from childhood to 25 years of age. It begins with weakness in leg and neck muscles and progresses to the upper leg, hands, and more neck muscles.
• Hereditary inclusion-body myositis (myopathy) type 1 (HIBM1): HIBM1 generally begins between the ages of 25 and 40. It starts affecting the thigh muscles and the muscles that are used to lift the top of the foot, later spreading out further.
• Miyoshi distal myopathy: Symptoms start between the ages of 15 and 30, with weakness in the lower extremities, especially the calves.
• Nonaka distal myopathy: Often in families of Japanese descent, symptoms begin between ages 20 and 40. First symptoms appear in the front lower leg muscles and then spread to the upper arm and leg and then the neck muscles.
• VCP (valosin-containing protein) myopathy (IBMPFD): Caused by a gene mutation that causes several conditions, it manifests as inclusion body myositis, Paget's disease of bone, or frontotemporal dementia. Individuals can have one, two, or all of the conditions.
• Welander distal myopathy: Symptoms start between ages 40 and 50 and usually affect the upper extremities and then the lower extremities.

Distal Muscular Dystrophy Symptoms

Specific symptoms can vary, depending on the subtype of DD that you have. In general, the first symptom is often weakness in the muscles farthest from the hips and shoulders, like hands, feet, and the lower part of the arms and legs. These are also known as the distal muscles.  

A signature symptom is progressive weakness and degeneration of the voluntary distal muscles. While other muscles may be affected over time, cognition and intellect are not affected by DD.

In the muscles that are affected, muscle wasting (atrophy) may occur, causing them to become smaller. Sometimes the muscles get so weak that mobility and range of motion are affected.

Different types of DD can affect different groups of muscles, causing varying symptoms, particularly as the condition progresses.

Causes

DD is an inherited condition, meaning it's passed down from parent to child. It can be either:

• Autosomal dominant: When only one parent has the abnormal gene
• Recessive: When both parents have the abnormal gene

There is no difference in risk between males and females. The distal myopathies are caused by a deficiency or absence of certain proteins that are important in the health and functioning of muscles. The specific diagnosis is based on which gene is affected or which mutation is present.

Diagnosing DD

Diagnosing any type of muscular dystrophy involves first taking a detailed medical and family history, and doing a physical exam. The exam is especially important in seeing any pattern of weakness.

Diagnostics includes the following:

• Nerve conduction studies and electromyography (EMG): These tests use electricity sent through needles inserted into muscles to evaluate the electrical activity in the muscles and nerves.
• Creatine kinase (CK) test: CK leaks out of damaged muscles, so when this enzyme is found in the blood, muscle damage is present for some abnormal reason. This test shows that it’s the muscles that are being affected by the weakness.
• Muscle biopsy: This may be done to further explore the results of the CK test. This involves taking a small piece of muscle and examining it in the lab. This can show the muscle proteins present, any abnormal levels of proteins, and if they’re in the right places, and it can give clues as to the genes that may be involved.
• Genetic testing: This is done with a blood sample. All forms of muscular dystrophy are inherited, and have different mutations or abnormalities. Genetic testing can help to determine the type of DD a person has.

Treatment

Right now, there is no cure for any form of DD. Treatment depends on the symptoms of the individual. Therapies can include:

• Physical therapy (PT): PT is used to increase muscle strength and keep range of motion (the measurement of movement around a joint). The specific activities can vary depending on the area of muscle weakness.
• Occupational therapy (OT): OT can help people adapt to everyday activities like eating, using the computer, and getting dressed. The therapist can show you how to use assistive devices, alternatives, or tools to aid with daily tasks.
• Braces or mobility devices: Devices like lower leg braces can help with symptoms such as foot drop (difficulty moving the front part of the foot), and other leg braces can provide support and stability. Power scooters, walkers, canes, and wheelchairs can make mobility easier and alleviate the fatigue of DD.
• Assistive devices for the computer/keyboard: These can help you type more easily if you have weakness in the hands and/or arms.

If an individual is having problems swallowing, assistance may be needed to prevent aspiration (when food or drink are breathed into the lungs) or choking (blocking of the airway). If the heart is affected, this must be monitored. Because each subtype can have such different symptoms, the therapies can vary widely, depending on a person’s needs.  

Prognosis

The prognosis for DD will depend on the subtype a person has. It also depends on the individual progression of the disorder. Some people experience slow progression and have a very mild disease course, while others may have significant weakness and impairment.

For instance, in Finnish muscular dystrophy, the ability to walk may be lost by the age of 30 because of muscle weakness. Conversely, in a condition like Welander distal myopathy, the muscle weakness can range from mild to severe, so those with mild weakness can retain mobility fairly well.

In Laing distal myopathy, the progression is so slow that even into an individual's 60s, wheelchairs or mobility aids are not needed. Someone with VCP disease will have comorbid conditions that can affect the brain or bone, impacting their prognosis.

Coping

Living with a progressive condition can be difficult, especially if it starts to interfere with your daily activities. Talk with your healthcare provider about finding a counselor or getting involved in a support group. It can help to have peers who understand what it’s like to live with DD, or who can provide guidance and tips for different stages of the disease.

A professional can also assess you for depression or anxiety if you have symptoms—both of which can impair your quality of life. There is help for these symptoms, and you can develop coping tools and strategies with support.

Summary

"Distal muscular dystrophy" is a term for a group of rare and progressive genetic muscular dystrophies. Symptoms can vary widely depending on the subtype. Although there is no cure for these conditions, treatment involves addressing the symptoms present with therapies to help with muscle strength.

Talk with your treatment team about the symptoms you may be having, what your disease course may look like, and the treatment options available to you.

A Word From Verywell

Living with any long-term condition isn’t easy, especially if it is progressive. Therapies, both physical and emotional, are available to support you. New research is being done all the time. If you’re interested in clinical trials, talk with your treatment team about whether that is a possibility for you.