Synonym/Acronym
AChR, AChR-binding antibody, AChR-blocking antibody, and AChR-modulating antibody.
Rationale
To assist in confirming the diagnosis of myasthenia gravis (MG) and monitor response to treatment.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
(Method: Radioimmunoassay) AChR-binding antibody: Less than 0.4 nmol/L; AChR-blocking antibody: Less than 25% blocking; and AChR-modulating antibody: Less than 45% modulating.
Study type: Blood collected in a red-top tube; related body system: Musculoskeletal system.
MG is an acquired autoimmune disorder that can occur at any age. Its exact cause is unknown. It seems to strike women between ages 20 and 40 yr; men appear to be affected later in life than women. It can affect any voluntary muscle, but muscles that control eye and eyelid movement, facial movement, and swallowing are most frequently affected.
Normally, when impulses travel down a nerve, the nerve ending releases a neurotransmitter called acetylcholine (ACh), which binds to receptor sites in the neuromuscular junction, eventually resulting in muscle contraction. There are three types of AChR autoantibodies:
- AChR-binding antibodies, which render ACh unavailable for muscle receptor sites, resulting in muscle weakness
- AChR-blocking antibodies, which impair or prevent ACh from attaching to receptor sites on the muscle membrane, resulting in poor muscle contraction
- AChR-modulating antibodies, which destroy AChR sites, interfering with neuromuscular transmission
Antibodies may not be detected in the first 6 to 12 mo after the first appearance of symptoms.
Testing for AChR-binding antibody is the most often requested of the three antibodies and is considered the initial test used to diagnose MG. The two other types of autoantibodies are rarely absent when binding antibody is detected.
Antibodies to AChR sites are present in 90% of patients with generalized MG and in 55% to 70% of patients who either have ocular forms of MG or are in remission. Approximately 10% to 15% of people with confirmed MG do not demonstrate detectable levels of AChR-binding, AChR-blocking, or AChR-modulating antibodies. Secondary testing is performed in these cases for anti-MuSK (muscle-specific receptor tyrosine kinase) antibody, which is produced in 40% to 70% of the remaining 15% who have MG but test negative for AChR autoantibodies.
MG is a common complication associated with thymoma. Remission after thymectomy is associated with a progressive decrease in antibody level. Other markers used in the study of MG include:
- Striational muscle antibodies
- Thyroglobulin
- Human leukocyte antigen (HLA)-B8
- HLA-DR3
A diagnosis of MG should be based on abnormal findings from two different diagnostic tests. These tests include:
- AChR antibody assay
- Anti-MuSK antibody assay (negative = less than 0.03 nmol/L)
- Edrophonium chloride test Prior to the edrophonium chloride test, the patient receives an injection of edrophonium chloride or Tensilon, a medication that temporarily blocks the degradation of acetylcholine. An MG-positive finding is indicated by normal measurable neuromuscular transmissions that dissipate as the effects of the injection wear off.
- Repetitive nerve stimulation Repetitive nerve stimulation testing involves sending small pulses of electricity, over and over, to specific muscles to measure a decreased response due to muscle weakening.
- Single-fiber electromyography (See EMG study for more detailed information.)
Factors That May Alter the Results of the Study
- Drugs and other substances that may increase AChR levels include penicillamine (long-term use may cause a reversible syndrome that produces clinical, serological, and electrophysiological findings indistinguishable from MG).
- Biological false-positive results may be associated with amyotrophic lateral sclerosis, autoimmune hepatitis, Lambert-Eaton myasthenic syndrome, primary biliary cholangitis, and encephalomyeloneuropathies associated with cancer of the lung. MG patients may also produce autoantibodies, such as antinuclear antibody and rheumatoid factor, not primarily associated with MG that demonstrate measurable reactivity.
- Immunosuppressive therapy may be recommended for treatment of MG; administration of immunosuppressive drug prior to testing may cause negative test results.
- Recent radioactive scans or radiation within 1 wk of the test can interfere with test results when radioimmunoassay is the test method.
Potential Nursing Problems: Assessment & Nursing Diagnosis
| Problems | Signs and Symptoms |
|---|
| Breathing (ineffective—related to increasing weakness, paralysis, respiratory muscle weakness, decreased diaphragm movement) | Shortness of breath, dyspnea, difficulty swallowing, aspiration, cyanosis, anxiety, hypoxemia, ineffective cough | | Fall, risk (related to impaired mobility, assistive device use, acute or chronic disease process, dizziness, confusion, history of previous falls) | Unsteady gait; decreased ability to complete activities of daily living independently, decreased visual acuity, or hearing; fatigue; weakness; difficulty following instructions; improper use of assistive devices; altered color perception; changed center of gravity; delayed response and reaction times | | Mobility (related to weakness, tremors, spasticity) | Unsteady gait, lack of coordination, difficult purposeful movement, inadequate range of motion | | Nutrition(insufficient—related to spasticity, altered level of consciousness, paresis, increasing weakness, paralysis) | Difficulty chewing, swallowing food; weight loss; decreasing amounts of food consumed; complaints of being too tired to eat; dysphagia (coughing or choking when eating or drinking); involuntary regurgitation (bringing food back up, sometimes through the nose) | | Self-care (deficit—related to spasticity, altered level of consciousness, paresis, increasing weakness, paralysis) | Difficulty fastening clothing and performing personal hygiene, inability to maintain appropriate appearance, difficulty with independent mobility, declining physical function | | Urination (altered—related to neurogenic bladder, spastic bladder; associated with disease process) | Urinary retention, urinary frequency, urinary urgency, pain and abdominal distention, urinary dribbling |
|
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test is used to identify antibodies responsible for decreased neuromuscular transmission and associated muscle weakness.
- Explain that a blood sample is needed for the test.
After the Study: Implementation & Evaluation Potential Nursing Actions
Avoiding Complications
- Discuss the importance of stating any prior reactions, complications, or family history of complications experienced with general anesthesia or cholinesterase inhibitors. Succinylcholine-sensitive patients may not metabolize anesthetics quickly, resulting in prolonged or unrecoverable apnea. If thymectomy is considered, the surgeon should be aware of this potential complication.
Treatment Considerations
- Explain that if a diagnosis of MG is made, a CT scan of the chest should be ordered to rule out thymoma.
Breathing
- Facilitate management of ineffective breathing and airway.
- Complete a thorough respiratory assessment including rate, rhythm, depth, chest expansion, breath sounds, and skin color to establish baseline for future comparison.
- Use high Fowlers position to enhance chest expansion.
- Administer ordered oxygen with humidification, evaluate with pulse oximetry.
- Administer ordered anticholinesterases, glucocorticoids, and antibiotics.
- Pace activities with collaborative input.
- Discuss techniques to evaluate swallowing effectiveness to prevent aspiration risk from muscle weakness that causes difficulty chewing and swallowing.
Fall, Risk
- Review medications to identify any pharmacological contributors to fall risk.
- Assess fall risk on admission, transfer, change of condition, and post-fall (if applicable).
- Follow established organizational fall prevention protocols.
- Identify previous fall history and frequency.
- Assess for disease-related symptoms such as orthostatic hypotension, urinary incontinence.
- Move the patient closer to the nurses’ station for easier observation.
- Enlist the support of reliable family members as partners in preventing falls.
- Move frequently used items close to the bed to decrease desire to get up.
- Answer call lights in a timely manner to decrease risk of getting up.
- Place the bed in the lowest possible position.
- Raise side rails judiciously as the situation requires.
- Encourage the use of well-fitting shoes with nonskid soles.
- Ensure the room is well lit to prevent tripping.
- Encourage the use of eyeglasses and hearing aids.
Mobility
- Keep the immediate environment cool to decrease aggravating MG symptoms.
- Use passive or active range of motion to decrease muscle tightness.
- Administer ordered analgesics, tranquilizers, antispasmodics, and neuropathic pain medication.
Self-Care
- Facilitate management of self-care deficits.
- Reinforce self-care techniques as taught by occupational therapy.
- Ensure there is adequate time to perform self-care.
- Encourage use of assistive devices to maintain independence.
- Assess ability to perform activities of daily living (ADLs). Provide care assistance appropriate to degree of disability while maintaining as much independence as possible.
Nutrition
- Facilitate management of insufficient nutrition.
- Monitor and trend albumin, electrolytes, glucose, total protein, and iron. Assess swallowing effectiveness.
- Recommend swallow evaluation as necessary.
- Consider a dietary consult.
- Discuss that the patient should sit up for meals and for 30 to 60 min afterward to prevent aspiration.
- Teach the family how to recognize choking signs and what to do if the patient begins choking.
- Facilitate small frequent meals.
- Allow enough time for meals and emphasize the importance of focusing on chewing and swallowing.
- Administer medications as ordered and exactly at the prescribed times: ACh inhibitors, analgesics, tranquilizers, antispasmodics, and neuropathic pain medication.
- Consider that some medications are most effective when given 30 to 60 min before meals to facilitate chewing and swallowing.
Urination
- Facilitate management of altered urinary function.
- Assess amount of fluid intake, as it may be necessary to limit fluids to control incontinence.
- Assess risk of urinary tract infection with limiting oral intake.
- Begin bladder training program.
- Discuss catheterization techniques to facilitate self-catheterization.
Safety Considerations
- Discuss how challenges with mobility can lead to risk for falls and injury.
- Recognize maintaining independence while preserving dignity and encouraging activities to improve muscle strength can be difficult.
- Assess gait, muscle strength, weakness and coordination, physical endurance, and level of fatigue prior to any activity.
- Assess the ability to perform safe independent movement.
- Discuss how placing self-care items within the patient’s reach can promote independence in care and may decrease injury risk.
Nutritional Considerations
- Assess for signs and symptoms of malnutrition or dehydration.
- Discuss meal plans, such as diets that offer soft solid foods or thick liquids, as provided by a registered dietitian or speech pathology consultant.
- Consider cultural food selections and foods that can be brought from home.
- Reinforce the importance of giving medications at the exact times recommended in relation to meal times.
Clinical Judgement
- Consider how interventions can be adapted to individualized deficits to enhance well-being and protect for injury.
Follow-Up and Desired Outcomes
- Acknowledges contact information provided for speech pathology services, emotional support with counseling services, or the Myasthenia Gravis Foundation of America (www.myasthenia.org) and the Muscular Dystrophy Association (www.mdausa.org)
- Recognizes the importance of adherence to recommended physical therapy including performance of range-of-motion activities, and acceptance of the physical limitations related to the disease process.