Myasthenia Gravis (MG)

Key Glossary Terms

Neurological Voice Disorders
Voice problems caused by abnormal control, coordination, or strength of voice box muscles due to an underlying neurological disease such as: stroke, Parkinson's disease, multiple sclerosis, myasthenia gravis, or ALS

Dysarthria
Difficulty forming words – presenting with imprecise consonants and hard-to-understand speech as seen with stroke patients

Speech Disorder
Malfunction of the tongue and/or lip muscles resulting in garbled words or parts or words.

Glossary

• The typical symptoms of myasthenia gravis involve the eyes, specifically double vision and drooping eyelids. The symptoms usually arise after repetitive tasks (due to muscle fatigue) and improve with short periods of rest.
• Voice and speech-related symptoms include:
  • Hoarseness
  • Vocal fatigue
  • Difficulty with controlling the pitch of the voice
  • Hypernasal voice
  • Mildly slurred speech
  • Monotone voice
  • Swallowing difficulty
  • Weakness of the jaw muscles

• Myasthenia gravis is an autoimmune disease affecting the nerve-muscle interface.
• The disease is more common in women (2:1). It typically presents between the ages of 30 and 40 in females and between the ages of 60 and 70 in males.
• No known risk factors exist.

• The most reliable method of diagnosis is a blood test that detects the abnormal antibodies to the nerve-muscle receptor. Some investigators have pointed out that these antibodies may be undetectable in cases of isolated laryngeal MG.
• Another method is the so-called "tensilon test." The muscle in question is fatigued by a repetitive task and edrophonium (tensilon) is given to dramatically, but temporarily, reverse the fatigue.
• Other tests look at the muscles' electrical firing (EMG) during repetitive tasks and their response to tensilon.

• The most common pitfall is a failure to recognize the often subtle symptoms of myasthenia gravis.
• Because vocal fatigue is such a common component of many other voice disturbances, an otolaryngologist may misdiagnose the patients' condition as muscle tension dysphonia, paresis of the vocal folds, or voice overuse/abuse.
• Evaluation by a neurologist should be obtained in unclear or unusual cases of vocal fold weakness or fatigue to rule out myasthenia gravis.

• MG is treated with medications called anticholinesterases (pyridostigmine or Mestinon), which restore muscle strength and reduce the tendency toward fatigue.
• In young patients recently diagnosed with MG or adult patients with a thymoma (a benign tumor in the thymus gland of the upper chest), a thymectomy may help control symptoms or lead to remission of the disease.
• With the current therapeutic options, myasthenia gravis is a disease that can be reasonably controlled without any effect on the patients' life expectancy.

Red Flag

Myasthenia gravis is felt by most laryngologists to be a rare cause of isolated hoarseness. Some laryngologists have described "isolated" MG of the larynx with hoarseness, vocal fatigue, reduced loudness, difficulty with pitch, and lack of vocal clarity – without any of the other eye, neck, jaw, or facial muscular weakness. These cases of "isolated" MG were mostly seronegative, meaning that the blood test for MG was negative. Many of the patients had improvement in their voice symptoms on MG medications, and subjective changes in their EMG testing that are somewhat compelling.

It remains to be seen whether MG is a more common cause of isolated voice problems.