Myasthenia Gravis

AUTHORS: Mitchell Powell, MD and Lydia Sharp, MD

Definition

Myasthenia gravis (MG) is an autoimmune disorder affecting postsynaptic neuromuscular transmission, most commonly mediated by antibodies directed against the nicotinic acetylcholine receptor (AChR) of the neuromuscular junction. Anti-AChR antibodies cause a decrease in functional postsynaptic ACh receptors, resulting in fatigable weakness. A small percentage of MG patients lack AChR antibodies, and a subset of these patients possess antibodies against muscle-specific tyrosine kinase (MuSK) or low-density lipoprotein receptor-related protein 4 (LRP4), which both affect pre- and postsynaptic function of the neuromuscular junction.¹^,² Finally, a portion of AChR antibody-negative myasthenia patients do not possess any detectable antibodies, and this group of patients is appropriately termed “seronegative.” A classification of MG is described in Table 1.

TABLE 1 Osserman Classification Used by the Myasthenia Gravis Foundation of America to Standardize Clinical Symptoms ¹

Class I		Any ocular muscle weakness
Class II		Ocular muscle weakness of any severity, MILD limb weakness
Class IIa		Predominantly limb and/or axial muscle weakness
Class IIb		Predominantly bulbar and/or respiratory muscle weakness
Class III		Ocular muscle weakness of any severity, MODERATE weakness of other muscles
Class IIIa		Predominantly limb and/or axial muscle weakness
Class IIIb		Predominantly bulbar and/or respiratory muscle weakness
Class IV		Ocular muscle weakness of any severity, SEVERE weakness of other muscles
Class IVa		Predominantly limb and/or axial muscle weakness
Class IVb		Predominantly bulbar and/or respiratory muscle weakness
Class V		Intubation with or without mechanical ventilation

¹Jaretzki A et al: Myasthenia gravis: recommendations for clinical research standards. Task Force of the Medical Scientific Advisory Board of the Myasthenia Gravis Foundation of America, Neurology 55:16-23, 2000.

From Parrillo JE, Dellinger RP: Critical care medicine: principles of diagnosis and management in the adult, ed 5, Philadelphia, 2019, Elsevier.

Synonym

ICD-10CM CODES
G70.00		Myasthenia gravis without (acute) exacerbation
G70.01		Myasthenia gravis with (acute) exacerbation
P94.0		Transient neonatal myasthenia gravis

Epidemiology & Demographics

Incidence (In U.S.)

8 to 10 cases annually per 1 million persons. It is the most common disorder of neuromuscular junction transmission.

Prevalence (In U.S.)

150 to 250 cases per 1 million persons.

Predominant Sex

Females are affected more often than males (3:2) in adults; they are equally affected in the elderly.

Peak Incidence

Female, second to third decades; male, sixth to eighth decades.

Genetics

Increased frequency of HLA-B8, DR3.

Physical Findings & Clinical Presentation

The hallmark of MG is weakness worsened with exercise and improved with rest.
Generalized weakness involving proximal muscles, the diaphragm, and neck extensors is common.
Weakness is confined to eyelids and extraocular muscles in approximately 15% of patients (Figs. 1, E2, 3, and Box 1). This is referred to as ocular myasthenia gravis.
Bulbar symptoms of ptosis, diplopia, dysarthria, and dysphagia are common.
Reflexes, sensation, and coordination remain normal.

Figure 1 Myasthenia gravis.

Myasthenia gravis may mimic any ocular disorder causing diplopia, although most often it mimics weakness of the superior rectus muscle or medial rectus muscle (i.e., difficulty with sustained elevation or adduction of the eye, respectively). Clues to the diagnosis of myasthenia gravis are associated ptosis, fluctuating course, and normal pupils.

From McGee S: Evidence-based physical diagnosis, ed 4, Philadelphia, 2018, Elsevier.

Figure 3 Typical myasthenic facies.

At rest (left), there is slight bilateral lid ptosis, which is partially compensated by asymmetric contraction of the frontalis muscle, raising the right eyebrow. During attempted smile (right), there is contraction of the medial portion of the upper lip and horizontal contraction of the corners of the mouth without the natural upward curling, producing a “sneer.”

From Jankovic J et al: Bradley and Daroff’s neurology in clinical practice, ed 8, Philadelphia 2022, Elsevier.

BOX 1 Ocular Findings in Myasthenia Gravis

Weakness usually involves one or more ocular muscles without overt pupillary abnormality.
Weakness is typically variable, fluctuating, and fatigable.
Ptosis that shifts from one eye to the other is virtually pathognomonic of MG.
With limited ocular excursion, saccades are superfast, producing ocular “quiver.”
After downgaze, upgaze produces lid overshoot (“lid twitch”)
Pseudo-internuclear ophthalmoplegia-limited adduction, with nystagmoid jerks in abducting eye.
In asymmetric ptosis, covering the ptotic eye may relieve contraction of the opposite frontalis.
Passively lifting a ptotic lid may cause the opposite lid to fall: “Enhanced ptosis” or “curtain sign.”
Edrophonium may improve only some of several weak ocular muscles; others may actually become weaker.
10.Edrophonium may relieve asymmetric ptosis and produce retraction of the opposite lid from frontalis contraction.
11.The opposite lid may droop further as the more involved lid improves after edrophonium.
12.Cold applied to the eye may improve lid ptosis: “Ice-pack test” (see Fig. E5).

From Jankovic J et al: Bradley and Daroff’s neurology in clinical practice, ed 8, Philadelphia, 2022, Elsevier.

Figure E2 Ocular Motility Abnormalities in Myasthenia Gravis Due to Weakness of Multiple Periocular Muscles in Both Eyes

(A and B) Progressive right lid ptosis during sustained forward gaze from fatigable weakness of the right levator palpebrae. (C) Attempted upward gaze. There is incomplete superior movement of both eyes, worse in the right eye. Note the asymmetric furrowing of the forehead and elevation of the eyebrows. (D) On left lateral gaze, there is skew deviation with incomplete medial movement of the right eye and incomplete abduction of the left eye. (E) On right lateral gaze, there is incomplete movement of both eyes from weakness of right lateral rectus and left medial rectus muscles.

From Jankovic J et al: Bradley and Daroff’s neurology in clinical practice, ed 8, Philadelphia 2022, Elsevier.

Etiology

An antibody-mediated decrease in nicotinic AChRs in the postsynaptic neuromuscular junction results in defective neuromuscular transmission and subsequent muscle weakness and fatigue. Early-onset MG is associated with HLA-B8.1, whereas late-onset MG is associated with HLA-DQB1, HLA-DQA1, and HLA-DRB1.³

Some myasthenia gravis patients present with MuSK or LRP4 antibodies instead of AChR antibodies. The MuSK antibody is present in about 40% to 50% of the subset of individuals who lack the AChR antibody, and the LRP4 antibody is present in a fraction of the remainder.¹ Both MuSK and LRP4 antibodies interrupt the process of AChR aggregation at the neuromuscular junction. Anti-MuSK patients have a similar syndrome to AChR MG, although they may have more bulbar weakness, facial tongue and proximal muscle atrophy, and either lack of or paradoxic response to pyridostigmine. Anti-LRP4 patients generally have milder symptoms that favor ocular findings. However, serious cases can still yield severe clinical symptoms.¹ Both MuSK and LRP4 antibody MG have not been shown to have any association with thymoma.⁴

Less than 10% of myasthenia gravis patients are seronegative for AChR, MuSK, and LRP4 antibodies. This syndrome is termed seronegative myasthenia gravis and presents with a higher proportion of entirely ocular symptoms. Generally, this group of patients responds well to classic MG therapies, including pyridostigmine, steroids, immunosuppression, and thymectomy.

Serologic and clinical presentation of myasthenia gravis subgroups are summarized in Table 2.

TABLE 2 Serologic and Clinical Presentation of Myasthenia Gravis Subgroups1-8

	AChR Antibody	MuSK Antibody	LRP4 Antibody	Striated Muscle Antigens Titin Antibody RyR Antibody	Age at Onset Sex	Clinical Findings	Response to Therapy	Response to Thymectomy	Prognosis
Ocular MG	50%-75%	None	None	None	Older Male	Ocular	Good	Good	Good (but 50% can develop generalized MG in 2 yr)
Early-onset generalized MG	80%-85% (high titer)	None	None	None-rare	<50 yr	General	Rarely needs immunosuppression	Good	Less severe Low mortality
Late-onset generalized MG	None-rare	None	None	50% 54% titin 33% RyR	≥50 yr	General	Often requires immunosuppression	Poor	Severe
Thymomatous-associated MG	Positive, nearly 100% (low titer)	None	None	95% 50% titin 47% RyR	Ranges: Older but <40 yr if RyR	General If RyR: Ocular, bulbar, respiratory weakness	Often requires immunosuppression	Fair	RyR: Invasive, malignant thymoma Severe Higher mortality
Generalized MG MuSK positive	None	100%	None	None	Younger female	Facial, bulbar, neck, respiratory weakness paraspinal, esophageal muscles	Poor response to AChE inhibitors	Poor (no thymic changes)	Severe, progressive course
Generalized MG LRP4 positive	None	None	100%	None	Younger female	General	Good	Not enough data	Fair
MG with thymic hyperplasia	89%	None	None	None	Younger female	General	Good	Good	Good
ACh antibody negative	Negative	Negative	Negative	Present	Younger female	General	Poor		Fair

ACh, Acetylcholine; AChE, acetylcholinesterase; AChR, acetylcholine receptor; MG, myasthenia gravis; MuSK, muscle-specific tyrosine kinase; LRP4, low-density lipoprotein receptor-related protein 4; RyR, ryanodine receptor.

¹Romi F et al: Myasthenia gravis patients with ryanodine receptor antibodies have distinctive clinical features, Eur J Neurol 14:617-620, 2007.

²Romi F et al: Myasthenia gravis: clinical, immunological, and therapeutic advances, Acta Neurol Scand 111:134-141, 2005.

³Akaishi T et al: Response to treatment of myasthenia gravis according to clinical subtype, BMC Neurol 16:225, 2016.

⁴Gilhus NE, Verschuuren JJ: Myasthenia gravis: subgroup classification and therapeutic strategies, Lancet Neurol 14:1023-1036, 2015.

⁵Hong Y et al: Autoantibody profile and clinical characteristics in a cohort of Chinese adult myasthenia gravis patients, J Neuroimmunol 298:51-57, 2016.

⁶Gilhus NE et al: Myasthenia gravis-autoantibody characteristics and their implications for therapy, Nat Rev Neurol 12:259-268, 2016.

⁷Roberts PF et al: Thymectomy in the treatment of ocular myasthenia gravis, J Thorac Cardiovasc Surg 122:562-568, 2001.

⁸Rivner MH et al: Clinical features of LRP4/agrin-antibody-positive myasthenia gravis: a multicenter study, Muscle Nerve 62(3):333-343, 2020. Available from https://doi.org/10.1002/mus.26985.

From Parrillo JE, Dellinger RP: Critical care medicine: principles of diagnosis and management in the adult, ed 5, Philadelphia, 2019, Elsevier.

Nonpharmacologic Therapy

Patient education to facilitate recognition of worsening symptoms and impress need for medical evaluation at onset of clinical deterioration
Avoidance of selected drugs (Table 3) known to provoke exacerbations of MG (β-blockers, aminoglycoside and quinolone antibiotics, penicillamine, interferons, class I antiarrhythmics [procainamide, quinidine, etc.])
Prompt treatment of infections, diet modification, and speech evaluation with dysphagia

TABLE 3 Medications to Avoid in Myasthenia Gravis ¹

Medications to Avoid	Examples	Recommendation for Avoidance	Mechanism of Weakness
Antibiotics
Aminoglycosides	Gentamycin Streptomycin	Contraindicated	Blocks ACh receptor, prevents release of ACh
Aminoglycosides	Tobramycin Amikacin	Less likely problematic	Blocks ACh receptor, prevents release of ACh
Antimalarials	Quinine Chloroquine	Contraindicated	Presynaptic blockage of voltage-dependent sodium channels and postsynaptic potentiation of depolarization
Macrolides	Erythromycin, Tetracycline Azithromycin	Relative	Affects presynaptic transmission
Fluoroquinolones	Moxifloxacin Ciprofloxacin Levofloxacin Ofloxacin	FDA black box warning	Unknown
Ketolide	Telithromycin	FDA black box warning	Unknown
	Polymyxins	Contraindicated	Presynaptic and postsynaptic effects
Cardiovascular
Antiarrhythmics	Procainamide Propafenone	Contraindicated	Decreases the release of AChSodium influx blocker
β-Blockers	Propranolol Atenolol Ophthalmic timolol	Relative	Unclear-may be at the neuromuscular junction or muscle membrane
Calcium channel blocker	Verapamil Amlodipine	Relative	Presynaptic and postsynaptic blockade of L-type calcium channels
Anticonvulsants
	Phenytoin	Relative	Depressed postsynaptic response to ACh; inhibition of calcium channel; increase in muscle membrane threshold
	Carbamazepine	Relative	Triggers immune response
	Gabapentin	Relative	Binds voltage-gated calcium channel
Chemotherapeutic Agents
	Doxorubicin Etoposide Cisplatin	Relative	Unknown
Others
	Interferon	Relative	Autoantibody production
Neuromuscular blocking agents	Atracurium Cisatracurium Vecuronium	Relative	Blocks ACh receptors
Statins		Relative	Unknown
Corticosteroids		Relative	Direct blocking of ACh receptor through ionic channels
Botulinum toxin		Contraindicated	Impairs synaptic transmission
Magnesium		Relative	Impairs synaptic transmission
Penicillamine		Contraindicated	Binds the ACh receptor; induces antibodies to receptor

ACh, Acetylcholine; FDA, Food and Drug Administration.

¹Ahmed A, Simmons Z: Drugs which may exacerbate or induce myasthenia gravis: a clinician’s guide, Internet J Neurol 10:1-8, 2008.

From Parrillo JE, Dellinger RP: Critical care medicine: principles of diagnosis and management in the adult, ed 5, Philadelphia, 2019, Elsevier.

Acute General Rx (Table E4

Symptomatic treatment with acetylcholinesterase inhibitors:
1. Pyridostigmine 30 to 60 mg PO q4 to 6h initially; onset of effect is 30 min, duration 4 h. May be titrated up to 120 mg every 4 h. GI upset is common with higher doses and may respond to hyoscyamine.
Immunosuppressive treatment with corticosteroids is first-line treatment, and is often transitioned to a nonsteroidal immunosuppressive agent such as azathioprine or mycophenolate to avoid the significant side effects of long-term steroid use:
1. Prednisone initiated at 10 to 20 mg daily titrated by 5-mg increments to effect or dose of 1 mg/kg/day with improvement in 2 to 4 wk and maximal response by 3 to 6 mo.
2. Azathioprine initiated at 50 mg daily titrated to 2 to 3 mg/kg/day with clinical effect in 6 to 12 mo. Azathioprine is not recommended in patients with no thiopurine methyltransferase activity.
3. Mycophenolate mofetil 500 mg twice a day titrated to 2 g/day with clinical effect in 3 to 6 mo, but can be up to 12 mo.
Targeted immunotherapy for myasthenia gravis allows quicker and more effective treatment with fewer side effects. Multiple new therapies are currently being researched and/or in clinical trials, including Fc receptor inhibitors, complement inhibitors, IL-6 inhibitors, chimeric antigen receptor (CAR) and chimeric autoantibody receptor (CAAR) T cell therapy, and hematopoietic stem cell transplantation.⁵ A current list of some alternative agents is below:
1. Efgartigimod alfa given at 10 mg/kg for 4 wk in weekly infusions with clinical effect within 1 mo. This drug is an Fc receptor inhibitor that promotes IgG degradation and was approved by the FDA in 2021. Further research is needed to determine the long term benefit of this drug, but it can be considered as a glucocorticoid-sparing bridge until slower-acting agents such as azathioprine and mycophenolate take effect.⁶
2. Ravulizumab initiated as IV infusion at 2.4-3 g (weight based) followed by 3-3.6 g (weight based) 2 wk after loading dose, followed by every 8 wk afterwards. This drug is a human monoclonal antibody that binds complement C5 similar to eculizumab but with a more convenient dosing schedule. It was FDA approved for AChR antibody positive patients in 2022.⁷
3. Eculizumab initiated at 900 mg IV weekly for four doses, then 1200 mg on the 5th wk and every 2 wk afterwards. Like ravulizumab, this drug is a complement inhibitor approved for adult patients who are acetylcholine-antibody positive and have severe symptoms despite current immunotherapy use.
4. Cyclosporine initiated at 5 mg/kg/day with clinical effect within 1 to 2 mo. Note a faster onset of effect than azathioprine or mycophenolate, but also a less tolerable side effect profile due to concerns for renal toxicity and drug interactions.
5. Tacrolimus initiated at 0.1 mg/kg/day divided into two doses then titrated to plasma concentration of 7 to 8 ng/ml with clinical effect within 6 to 12 mo. This drug is better tolerated than cyclosporine but still has potential for serious side effects.
6. Rituximab initiated at 1 g every 2 wk for two doses, OR 375 mg/m² weekly for four doses. Generally used in refractory MG or earlier in MuSK antibody MG. Redosing interval varies per protocol and by clinical response of the patient.
Plasmapheresis and IV immunoglobulin (IVIG) are short-term options for immunotherapy during an exacerbation. There is no significant difference in efficacy between IVIG and plasmapheresis.⁸
Mechanical ventilation is lifesaving in the setting of a myasthenic crisis. Consider elective intubation if forced vital capacity is <10 to 15 ml/kg.
Fig. E6 illustrates a flowchart for the management of myasthenic crisis.

Figure E6 Clinical flowchart for the management of myasthenic crisis.

ABG, Arterial blood gas; AChE, acetyl cholinesterase; BiPAP, bilevel positive airway pressure; ICU, intensive care unit; IVIG, intravenous immunoglobulin; PFT, pulmonary function test.

From Parrillo JE, Dellinger RP: Critical care medicine, principles of diagnosis and management in the adult, ed 4, Philadelphia, 2014, Elsevier.

Table E4 Therapeutic Agents Used in Myasthenia Gravis

Agent	Initial Dose	Maintenance Dose	Onset of Action	Major Adverse Events	Monitoring	Comments
Pyridostigmine	30-60 mg tid	60-120 mg tid to 5×/day, adjusted based on symptoms, typically not to exceed 480 mg/day	15-30 min	Stomach cramps, nausea, vomiting, diarrhea, muscle twitching and cramps, sweating, salivation, blurred vision	Use the minimal amount that produces clinical improvement; this is best achieved by using a dose that produces observable improvement after most administrations	Can counter muscarinic adverse events with anticholinergic agents (i.e., glycopyrrolate, hyoscyamine sulfate, propantheline, diphenoxylate HCl with atropine, or loperamide)
Prednisone	Option 1: 10-20 mg/day, increasing daily dose by 5 mg daily equivalent every week until treatment goal achieved Option 2: Start at 50-80 mg/day; this approach may require inpatient hospitalization (see text for details)	Slow alternate day taper after treatment goal achieved for several days (see text for details). Taper more slowly once ≤10 mg/day dose equivalent. Continuing a low dose long-term can help to maintain the treatment goal	2-4 wk	Hypertension, diabetes, weight gain, bone loss, cataracts, GI ulcers, glaucoma, neuropsychiatric symptoms, growth retardation in children, hypothalamic-pituitary axis suppression	HbA_1c every few months, blood pressure checks, bone density monitoring, eye exam for glaucoma and cataracts	Administer in single morning dose; temporary worsening is seen in up to 50% of patients, starting on high doses and in some patients on lower doses; IVIg or PLEX may prevent steroid-induced worsening
Azathioprine	50 mg/day	Increase by 50 mg increments every 1-2 wk to target of 2.5-3 mg/kg/day	2-10 mo for initial response. Up to 24 mo for maximum benefit	Fever, abdominal pain, nausea, vomiting, anorexia, leukopenia, hepatotoxicity, skin rash	CBC, LFTs 1-4 times in first mo, then monthly to every third month. Regular dermatologic examinations if taken chronically	10% of patients cannot tolerate because of flulike reaction; major drug interaction with allopurinol; TPMT enzyme testing can be performed, if available, before starting treatment to identify patients at high risk of bone marrow suppression
Cyclosporine	100 mg bid	Increase slowly as needed to 3-6 mg/kg/day on bid schedule.	1-3 mo	Hirsutism, tremor, gum hyperplasia, hypertension, hepatotoxicity, nephrotoxicity, PRES	CBC, LFTs, BUN/Cr monthly ×3, then every 3 mo; monitor trough drug levels	Bioequivalence differs between preparations, so avoid brand switching when possible; grapefruit juice may increase blood level; high potential for drug-drug interactions
Mycophenolate mofetil	500 mg bid	1000-1500 mg bid	2-12 mo	Diarrhea, vomiting, leukopenia, teratogenicity (black box warning)	CBC weekly for 4 wk, every 2 wk for 4 wk, then monthly to every 3rd mo; REMS program when used in women of childbearing age	Diarrhea may resolve by change to tid dosing
Efgartigimod alfa	10mg/kg qwk x 4 wk	Efficacy of repeated cycles unclear	1 mo	Headache, infections	BMP	Approved for AChR Ab MG only. Possible glucocorticoid-sparing bridge
Ravulizumab	2.4-3g IV	3-3.6g IV 2 wk then q8wk afterwards	1-2 mo	Upper respiratory infections, leukopenia, transaminitis, meningococcal meningtitis	CBC, LFTs; monitor for signs of meningitis	Easier dosing than Exulizumab. Approved for AChR Ab MG only, when continued symptoms despite other therapies. Meningococcal vaccination at least 2 wk prior-if not possible, then antimicrobial prophylaxis recommended
Eculizumab	900 mg IV weekly × 4 wk	1200 mg IV q2wk	1-2 mo	Upper respiratory infections, leukopenia, transaminitis, meningococcal meningtitis	CBC, LFTs; monitor for signs of meningitis	Approved for AChR Ab MG only, when continued symptoms despite other therapies. Meningococcal vaccination at least 2 wk prior-if not possible, then antimicrobial prophylaxis recommended
Cyclophosphamide	(1) Oral: 50 mg/day(2) IV: 500 mg/m² monthly	Oral: Increase by 50 mg/wk to maintenance dose of 2-3 mg/kg/day	2-6 mo	Alopecia, leukopenia, nausea and vomiting, skin discoloration, anorexia, hemorrhagic cystitis, malignancy	CBC, BUN/Cr, electrolytes, LFTs, urinalysis every 2-4 wk	IV pulse therapy may be less toxic because cumulative dose is lower
Tacrolimus	3-5 mg/day or 0.1 mg/kg/day	Increase dosing as needed for response following trough levels (see last column)	1-3 mo	Hyperglycemia, hypertension, headache, hyperkalemia, nephrotoxicity, diarrhea, nausea, vomiting, PRES	BUN/Cr, glucose, K⁺; trough drug levels every few weeks initially, then less frequently	Insulin-dependent diabetes mellitus developed in 20% of postrenal transplant patients; trough levels of 8-9 ng/ml may be effective
Methotrexate	5-15 mg weekly for 2 wk	Increase by 5 mg every 2 wk to a maximum dose of 15-25 mg weekly	2-6 mo	Leukopenia, mouth ulceration, nausea, diarrhea, headaches, hair loss, hepatotoxicity, pulmonary fibrosis, rare nephrotoxicity, teratogenicity	CBC, LFTs monthly initially, then at least every 3 mo. Monitor periodically for interstitial lung disease, a rare occurrence with doses used for immunotherapy	Consider folic acid 5 mg/day to reduce toxicity. Absolutely contraindicated in pregnancy
Intravenous immunoglobulin (IVIg)	2 g/kg over 2-5 days	0.4-1 g/kg every 4 wk; can attempt to decrease frequency over time	1-2 wk	Headache, aseptic meningitis, nephrotoxicity, ischemic events, fluid overload, leukopenia, thrombocytopenia	BUN/Cr every month, decreasing to every 3rd mo over time	IgA level before starting treatment may be useful to identify congenital IgA deficiency, a contraindication to IVIg use; avoid in patients with recent thrombotic/ischemic event. Use sucrose-free formulation for patients at risk of renal toxicity

BUN/Cr, Blood urea nitrogen/creatinine; CBC, complete blood count; GI, gastrointestinal; IgA, immunoglobulin A; IV, intravenous; LFTs, liver function tests; PLEX, plasma exchange; REMS, risk evaluation and mitigation strategy; TPMT, thiopurine s-methyltransferase.From Sanders DB et al: International consensus guidance for the management of myasthenia gravis: executive summary, Neurology 87:419-425, 2016.

Surgical Rx

In thymomatous MG, thymectomy is indicated in all patients. If the tumor cannot be surgically resected, chemotherapy can be considered for prevention of local invasion and symptom relief.
For nonthymomatous AChR-antibody positive MG, thymectomy improves clinical outcomes and reduces the need for steroids sustained over at least a 5-yr period. Surgical referral should be considered in patients <60 yr old without significant medical comorbidities even if no frank thymic tissue is seen on imaging, especially if they are refractory to therapy.⁹^,¹⁰
MuSK and LRP4 myasthenia are not associated with thymic pathology and generally thymectomy is not beneficial for these patients.¹¹

Disposition

Course of disease is highly variable. Mortality rate has decreased from 75% to 4.5% over the past four decades.

Referral

Referral to a general neurologist or neuromuscular specialist is appropriate.
Surgical referral for thymectomy in selected cases (see “Surgical Rx”).

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Basic Information ⬇

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