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FACT SHEET: Myasthenia Gravis (also known as “MG”)

Date of Publication: March 5, 2019

Is the initiation of non-invasive dental hygiene procedures* contra-indicated?

  • No.

Is medical consult advised?

  • Possibly (depends on severity and level of control of the disease, including manifestations that may interfere with oral examination and manipulation). Initial clinical suspicion of MG warrants referral for definitive diagnosis1, and progression of signs/symptoms warrants referral for potential alterations to medical treatment.

Is the initiation of invasive dental hygiene procedures contra-indicated?**

  • Possibly.

Is medical consult advised?

  • See above. Additionally, medical consultation may be indicated for potential pre-procedure administration of anticholinesterase medication to mitigate against anticipated muscle weakness during procedures.

Is medical clearance required?

  • Possibly (e.g., if the disease is poorly controlled, with resultant respiratory compromise and/or muscle weakness that interferes with oral examination or manipulation). Also, medical clearance may be required if patient/client is being treated with medications associated with immunosuppression +/- increased risk of infection (e.g., corticosteroids [e.g., prednisone], azathioprine, mycophenolate mofetil, tacrolimus, cyclosporine, rituximab, and eculizumab).

Is antibiotic prophylaxis required?

  • No, not typically (although extended use of corticosteroids may warrant consideration of antibiotic prophylaxis).

Is postponing treatment advised?

  • Possibly, but not typically (depends on severity and level of control of disease, including presence/absence of manifestations that interfere with oral examination and manipulation, as well as medical clearance for patients/clients on medications associated with immunosuppression). Treatment should be postponed if the patient/client has severe dyspnea until shortness of breath has resolved; in particular, a myasthenic crisis2 is a medical emergency and immediate medical attention is required. Treatment should also be postponed and prompt medical attention obtained if a cholinergic crisis3 is suspected.

Oral management implications

  • Because chewing difficulty can develop before the noticeable onset of other signs/symptoms, the oral healthcare professional may be in a position to first detect MG. This provides an opportunityfor early referral for definitive diagnosis and treatment. As well, the dental hygienist may note disease recurrence or progression during longitudinal appointments.
  • Facial and masticatory muscles may be involved, which can complicate dental hygiene care. Even in well controlled patients/clients, treatment modifications may be required to avoid exacerbation of the underlying disease.
  • An assessment should be made of the patient/client’s abilities to swallow, speak, and breathe4. Treatment, communication, and education should be tailored accordingly.
  • The stable patient/client with limited or mild neuromuscular involvement can usually be treated safely in the private dental/dental hygiene office setting. However, the patient/client with frequent exacerbations or significant pharyngeal, respiratory, or generalized weakness may most appropriately receive dental/dental hygiene care in a hospital dental clinic or other facility with emergency intubation and respiratory support capabilities. Preoperative plasmapheresis (plasma exchange) may be indicated in the patient/client with frequent severe myasthenic exacerbations who is anticipated to undergo significant oral surgery5.
  • Patients/clients on long-term corticosteroids should be considered immunosuppressed.
  • Early morning appointments should be scheduled, because patients/clients typically have greater muscle strength during the morning hours. Multiple short-duration appointments are usually more appropriate than one extended appointment. Frequent rest breaks may be required.
  • In consultation with the patient/client’s physician6, oral anticholinesterase agents may be appropriate to administer before dental or dental hygiene procedures (typically 1 to 2 hours prior to procedures to achieve maximal effects during procedures).
  • Nitrous oxide oxygen sedation may reduce stress associated with dental treatment.
  • Head droop may necessitate increased incline of the dental chair or other positioning modifications. However, a pronounced reclining position may induce a feeling of throat closure, difficulty breathing, and/or difficulty handling secretions; hence, many patients/clients with MG benefit from a more upright position. Communication of any distress should be encouraged.
  • In patients/clients with significant respiratory muscle involvement, dyspnea may necessitate breaks from, or cessation of, procedures. Respiratory rate and depth of respiration should be monitored.
  • Aspiration is a risk during procedures due to weakness of the oral and pharyngeal musculature. Appropriate suction should be used for oral secretions.
  • Because anticholinesterase medications can cause saliva flow to increase, the dental hygienist or dentist can use a low speed saliva ejector to collect saliva during treatment. Alternatively, high-speed evacuation suction can be used to collect saliva and debris.
  • The dental hygienist should be alert to signs of a myasthenic crisis, which constitutes a medical emergency. Severe bulbar (oropharyngeal) muscle weakness often accompanies respiratory muscle weakness or may be the predominant feature in some patients/clients. When this results in upper airway obstruction or severe dysphagia with aspiration (particularly in combination with atelectasis), intubation and mechanical ventilation are necessary.
  • The dental hygienist should be alert to signs of a cholinergic crisis, which requires prompt medical attention. Hyper-salivation is a feature.
  • A significant exacerbation of MG signs/symptoms in the dental hygiene office should prompt physician evaluation for severity of neuromuscular involvement.
  • Finger, hand, and arm weakness may necessitate modified, and/or assistance with, toothbrushing and other oral self-care activities. An electric toothbrush or manual toothbrush with modified handle that is easy to grasp will reduce muscle fatigue.
  • To reduce chewing and swallowing difficulties, the patient/client can be encouraged to eat the main meal of the day in the morning when muscles are strongest. A half-hour rest period before meals and frequent rests while eating can also be beneficial. In consultation with the patient/client’s physician, the patient/client may benefit from taking an anticholinesterase medication 1 hour before meals.
  • The patient/client’s ability to manage dentures may be compromised by the inability of weak muscles to assist in the retention of a lower denture and to maintain a peripheral seal for an upper denture. Improperly fitting dentures can exacerbate the following: difficulty in closing the mouth; tongue fatigue; tightness in the upper lip; dysphagia; impaired phonation; and masticatory problems.
  • Exacerbation of muscle weakness, fatigability, or breathing ability can be precipitated by certain drugs used in dentistry7. Generally safe drugs for MG patients/clients include acetaminophen, non-steroidal anti-inflammatory drugs (NSAIDs; unless cyclosporine is being used), acetylsalicylic acid (ASA), nitrous oxide oxygen sedation, and penicillin and its derivatives8.
  • When having restorations done by a dentist, a rubber dam can be used to isolate teeth and keep water and restorative materials from getting near the throat.

Oral manifestations

  • Weakness in the muscles used for chewing, swallowing, and talking is common.
  • Mouth drop can occur due to lack of muscle strength in the masseter muscles, particularly after sustained chewing effort (e.g., part-way through a meal when eating steak). Poor masticatory performance is seen in patients/clients with bulbar MG, similar to that seen in persons with progressive muscular dystrophy and some forms of cerebral palsy. A minority of patients/clients with MG first present with a fatigable reduction in biting force.
  • Dysphagia leads to choking, and liquids being swallowed may come out the nose.
  • Dysarthria may manifest as very soft or nasal-sounding speech, depending on which muscles are affected.
  • The facial muscles are commonly involved, giving the patient/client an immobile, expressionless appearance. Family members may comment that the patient/client has lost his/her smile.
  • In addition to manifesting muscle weakness, the tongue may have a furrowed, flaccid appearance due to lipomatous atrophy. In severe cases, triple longitudinal furrowing can occur.
  • Chronic oral candidiasis is seen in patients in patients/clients with thymoma9 (due to dysfunctional cellular immunity), as well as following thymectomy (and adjuvant radiation therapy and/or chemotherapy).
  • Gingival hyperplasia can result from cyclosporine use.

Related signs and symptoms

  • MG is a chronic autoimmune neuromuscular disorder10 of unknown etiology, which results in weakness and irregularly rapid fatigue of voluntary muscles upon exertion.
  • About 20 to 26 out of 100,000 people worldwide have myasthenia gravis. In Ontario, more than 3600 residents are estimated to live with MG. Prevalence is rising with stable incidence over time, which is likely reflective of patients living longer due to improved treatment. Although MG can affect persons of any age, incidence is highest in women between 20 and 40 years of age and in men between 50 and 70 years of age11. There is no known cure. MG occurs about twice as often in females than in males.
  • The onset of MG may be sudden, with severe and generalized muscle weakness, but more frequently the early signs/symptoms are subtle and variable. The hallmark is skeletal muscle weakness that worsens after activity and improves after rest.
  • There are two clinical forms of MG; namely, ocular myasthenia (in which weakness is limited to the eyelids and extraocular muscles) and generalized disease (in which weakness commonly affects ocular muscles as well as a variable combination of bulbar [i.e., oropharyngeal], limb, and respiratory muscles).
  • The first noticeable sign is often eye muscle weakness, which manifests as ptosis and/or blurred vision or diplopia (double vision). In some patients/clients, the disease remains confined to the eye muscles, but in most persons it progresses to other muscles served by other cranial nerves as well as to the shoulders and limbs.
  • Other signs/symptoms may include: severe fatigue; unstable or waddling gait; arm weakness (sometimes resulting in an inability to raise the arms over the head); hand and finger weakness; and dyspnea and breathing difficulty.
  • Signs/symptoms improve with rest.
  • Management options include corticosteroids, immunosuppressive drugs, anticholinesterase medications (e.g., pyridostigmine and neostigmine), thymectomy, plasmapheresis, and intravenous immune globulin (Ig). In severe cases of respiratory muscle involvement, intubation and ventilatory support may be required in the hospital setting.
  • Pneumonia can result from aspiration.
  • Poor nutrition, dehydration, and hypokalemia (low serum potassium level) can result from impaired mastication and dysphagia.
  • Some persons with MG may go into temporary or permanent remission, and medications can be discontinued. Stable, long-lasting remission is the goal of thymectomy.
  • Formerly considered a terminal disease, the mortality rate is now low in patients/clients receiving optimal care. With treatment, most patients/clients can lead normal or nearly normal lives. However, MG can still be life-threatening when severe muscle weakness causes respiratory failure.
  • Patients/clients with MG are more likely to have other autoimmune conditions, including rheumatoid arthritis and lupus erythematosus. Hypothyroidism and hyperthyroidism also occur at elevated rates.

References and sources of more detailed information

Date: April 25, 2018
Revised: May 5, 2023


1 MG is usually definitively diagnosed by a neurologist or another internal medicine specialist.
2 A myasthenic crisis is a life-threatening condition that can involve weakness of the upper airway muscles, respiratory muscles, or a combination of both muscle groups. Inspiratory and expiratory muscles can both be affected, manifesting as severe dyspnea. Respiratory failure is severe enough to require intubation and mechanical ventilation. Triggering factors include stress (physical, environmental, and emotional), surgery, infection, pain, temperature extremes, aspiration pneumonitis, sleep deprivation, perimenstrual state, pregnancy, and adverse drug reaction (involving some antibiotics, certain anaesthetics, anti-epileptics, beta blockers, calcium channel antagonists, quinidine, quinine, and corticosteroids [particularly upon initiation], amongst others). Up to 20% of patients/clients with MG experience at least one myasthenic crisis.
3 A cholinergic crisis may result from the patient/client taking an excess of anticholinesterase inhibitors. In addition to increased oral secretions, signs/symptoms include diaphoresis (excessive sweating), increased pulmonary secretions, nausea, vomiting, diarrhea, bradycardia, and muscle fasciculations and weakness. Administration of atropine may be required.
4 The amount of time the patient/client can look up before ptosis (drooping eyelids) and the length of time the patient/client can maintain outstretched arms are quick measures of disease severity.
5 If the patient/client’s plasma exchange protocol involves use of anticoagulants, dental treatment should be arranged for a non-exchange day in the treatment sequence.
6 Patients/clients with MG are typically followed by a neurologist.
7 The following drugs are relatively contraindicated: procaine, erythromycin, clindamycin, gentamicin, neomycin, polymyxin B, and bacitracin. The following drugs should be used with caution: lidocaine, mepivacaine, bupivacaine, prilocaine, morphine and its derivatives, narcotics, benzodiazepines, hypnotics, barbiturates, metronidazole, tetracycline, and vancomycin.
8 Ampicillin has been occasionally implicated as a precipitant of myasthenic crisis.
9 A thymoma is a tumour of the thymus (a small lymphoid organ found in the upper chest underneath the sternum), which is found in about 20% patient/clients with myasthenia gravis. Initial management is usually surgical removal (thymectomy), potentially followed by chemotherapy and adjuvant radiation therapy.
10 In the most common form of MG, the immune system attacks the acetylcholine (ACh) receptor sites at the post-synaptic neuromuscular junction; this results in an error of transmission of nerve impulses to muscles. In another form of MG, usually seen in young women, the immune system attacks muscle-specific tyrosine kinase (MuSK), a protein involved in forming the neuromuscular junction.
11 In addition to physical and neurological examinations, diagnosis of MG is established via one or more of: an edrophonium test (i.e., injection of a drug that blocks the breakdown of acetylcholine); a blood test (for antibodies against acetylcholine receptors and/or MuSK); electrodiagnostics (e.g., electromyography); diagnostic imaging (e.g., computed tomography [CT] scan or magnetic resonance imaging [MRI] to identify the presence of a thymoma); and pulmonary function testing (to measure breathing strength).

* Includes oral hygiene instruction, fitting a mouth guard, taking an impression, etc.
** Ontario Regulation 501/07 made under the Dental Hygiene Act, 1991. Invasive dental hygiene procedures are scaling teeth and root planing, including curetting surrounding tissue.