Oculopharyngeal Muscular Dystrophy (OPMD) is a rare, inherited neuromuscular disorder causing progressive weakness in specific muscles. This condition is characterized by a slow decline in muscle function that typically does not begin until a person reaches adulthood. OPMD primarily affects the muscles responsible for moving the eyes and swallowing, requiring individuals to manage increasing physical limitations.
The Genetic Basis and Onset
The underlying cause of OPMD is a genetic change within the PABPN1 gene. This gene provides instructions for making a protein involved in RNA processing. A mutation in this gene, most commonly inherited in an autosomal dominant pattern, results in an expanded polyalanine tract in the protein structure.
The altered protein becomes defective and starts to form insoluble clumps called intranuclear aggregates inside the muscle cell nuclei. These protein aggregates are a hallmark of OPMD and impair the normal function of the muscle cells, leading to their progressive weakness. Although an individual is born with the genetic mutation, the muscle weakness and symptoms typically do not manifest until later in life, usually between the ages of 40 and 60.
Primary Clinical Manifestations
The initial and most characteristic signs of OPMD are concentrated in the muscles around the eyes and throat. The first symptom to appear is often ptosis, which is the drooping of the upper eyelids. This drooping is usually bilateral and can be severe enough to obstruct a person’s vision.
To compensate for the impaired sight, people with OPMD often adopt a posture of tilting their head back and raising their eyebrows to lift their eyelids manually. In some cases, the muscles that control eye movement can also weaken, which may lead to restricted eye movement and occasionally double vision. Following the onset of ptosis, or sometimes concurrently, difficulty swallowing, known as dysphagia, begins to develop.
Dysphagia makes the passage of food and liquid difficult. Individuals may first notice problems with dry or solid foods, feeling like something is stuck in their throat. As the condition advances, even swallowing liquids, including saliva, can become a challenge, increasing the effort and time required to complete a meal.
Disease Progression and Secondary Effects
While OPMD is defined by its primary effects on the eyes and throat, the muscle weakness slowly extends to other parts of the body. Weakness often begins in the proximal limb muscles, such as the hips and upper legs. This weakening can make everyday actions increasingly difficult, such as climbing stairs, rising from a low chair, or squatting.
Mobility issues may develop over time, potentially requiring a cane or walker. Though less common, weakness can eventually spread to the arms and lower legs, and in severe cases, individuals may eventually require a wheelchair. The most serious secondary effects arise from the chronic swallowing difficulty.
Dysphagia increases the risk of food or liquid inadvertently entering the lungs, a complication called aspiration. This aspiration can lead to repeated lung infections, specifically aspiration pneumonia. Furthermore, the difficulty and reluctance to eat due to swallowing problems can result in chronic weight loss and poor nutrition.
Diagnosis and Symptom Management
The process of identifying OPMD usually begins when a healthcare provider observes the characteristic combination of ptosis and dysphagia in an adult. The diagnosis is most reliably confirmed through a blood test that looks for the specific expansion in the PABPN1 gene. Genetic testing has largely replaced the need for a muscle biopsy.
Currently, there is no cure for OPMD, so management focuses on alleviating symptoms and preventing complications.
Managing Dysphagia
Initial interventions for difficulty swallowing include:
- Working with a speech-language pathologist to learn modified swallowing techniques.
- Adjusting the texture of foods.
- Considering a cricopharyngeal myotomy, which involves surgically cutting a throat muscle to ease food passage.
Ptosis can be managed with glasses fitted with special supports called ptosis crutches, or through eyelid surgery, known as blepharoplasty. For the limb weakness, physical and occupational therapy can help individuals maintain strength, flexibility, and independence. Therapists can suggest assistive devices, like walkers or canes, to help with mobility as the disease progresses.