Can myasthenia gravis (MG) be diagnosed at age 76?

Myasthenia Gravis Can Be Diagnosed at Age 76

Yes, myasthenia gravis can absolutely be diagnosed at age 76, as there is no upper age limit for the onset of this autoimmune disorder. 1 In fact, myasthenia gravis demonstrates a bimodal age distribution, with males typically developing the condition at older ages compared to females 2.

Epidemiology and Presentation in Elderly Patients

• Myasthenia gravis has an incidence ranging from 0.04 to 5/100,000 per year, with prevalence estimates of 0.5 to 12.5/100,000 per year 1
• While onset in adults is typically in the third to fourth decade, it can occur "much later in males" 1
• The disease is often underdiagnosed in elderly populations, with diagnosis frequently delayed (mean delay of 31±47 months in one study of elderly patients) 3

Clinical Presentation in Elderly Patients

Elderly patients with myasthenia gravis may present with:

• Ocular symptoms (35% of elderly cases) - ptosis and variable strabismus 3
• Bulbar and ocular symptoms combined (39% of elderly cases) - difficulty swallowing, speaking 3
• Generalized weakness (26% of elderly cases) 3
• Fatigable muscle weakness that worsens with repetitive use 1
• Variable incomitant strabismus accompanied by variable ptosis 1
• Dysphagia and weight loss that may be mistaken for other age-related conditions 4

Diagnostic Approach for Suspected MG at Age 76

1. Clinical Tests:

   • Ice pack test: Application over closed eyes for 2 minutes (ptosis) or 5 minutes (strabismus) may show reduction of symptoms 1
   • Rest test: Observation of symptom improvement after rest 1
   • Cogan lid-twitch sign: Abnormal lid movement after downward gaze 1

2. Laboratory Testing:

   • Anti-acetylcholine receptor antibodies (AChR-Ab): Present in 80-85% of all MG patients, but only in 83% of elderly MG patients 3, 2
   • Anti-MuSK antibodies: Important to check in AChR-negative cases 1, 5
   • Anti-LRP4 antibodies: May be present in some seronegative cases 2

3. Electrophysiological Studies:

   • Repetitive nerve stimulation testing: Positive in only one-third of ocular myasthenia cases 1
   • Single-fiber electromyography: Considered the gold standard for diagnosis, positive in over 90% of ocular myasthenia cases 1

4. Additional Workup:

   • Chest imaging to evaluate for thymoma (less common in elderly-onset MG) 3
   • Pulmonary function assessment if respiratory involvement is suspected 1

Management Considerations in Elderly MG Patients

1. First-line Treatment:

   • Pyridostigmine (Mestinon): Starting at 30mg three times daily, gradually increasing to maximum 120mg four times daily as tolerated 1
   • Note: About half of patients with strabismus-associated myasthenia show minimal response to pyridostigmine 1

2. Immunosuppressive Therapy:

   • Corticosteroids: 66-85% of patients show positive response 1
   • Steroid-sparing agents: Azathioprine or mycophenolate mofetil may be necessary in elderly patients 3

3. Advanced Therapies for Refractory Cases:

   • Intravenous immunoglobulins (IVIG) 3
   • Plasma exchange 3
   • Rituximab for MuSK-positive MG 5
   • Efgartigimod alfa-fcab (recently FDA approved for AChR-positive patients) 1

4. Thymectomy:

   • Always indicated in the presence of thymoma 1
   • May substantially reduce symptoms for certain subpopulations 1
   • Less commonly performed in elderly patients (only 1 of 23 patients in one elderly cohort) 3

Special Considerations for Elderly Patients

• Diagnosis is often missed or delayed due to the broad differential diagnosis in older people 3
• Stroke is frequently considered before MG in elderly patients with ocular or bulbar symptoms 3
• Medication review is crucial as certain drugs can worsen MG: beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics 1
• Careful anesthetic management is required if surgery is needed, as respiratory muscles may be affected 1

Prognosis

While myasthenia gravis in elderly patients can be challenging to manage, with appropriate diagnosis and treatment, patients can achieve good quality of life 3, 6. However, the condition should not be underestimated, as some elderly patients may require intensive care admission and the condition can be fatal if not properly managed 3, 4.