Any patient with MG should be investigated for other autoimmune diseases such as endocrine diseases (thyroid disorders), rheumatoid arthritis, ulcerative colitis, and sarcoidosis, as these disorders are frequently encountered [9]. As previously mentioned, malnutrition due to dysphasia or hypothyroidism as a result of autoimmune disease requires extra attention from the anesthesiologist as they may affect postoperative recovery. If detected, these conditions must be treated prior to surgery.

Several conditions that may exacerbate the course of disease and may even cause the need for mechanical ventilation are reported. Infections, thyroid disorders, radiation, and extreme temperature are frequent pathological risk factors; however, sleep disorders, pain, or menses may also worsen patient’s status [6, 9]. Besides drugs which may affect/weaken neuromuscular junction, a large variety may aggravate the course of the disease in a dose-dependent manner with antibiotic [e.g., aminoglycosides], antiarrhythmic [e.g., verapamil], and neuropsychiatric agents (Table 8.2). Although corticosteroid is a part of the therapy, it may paradoxically cause an early exacerbation of MG. If surgery should be performed at initial phase of steroid therapy, anesthetist must be aware of this worsening effect [10].

Besides drugs, electrolyte imbalances may be associated with increased muscle weakness. Hypermagnesemia is the most prominent cause as magnesium acts as an antagonist to calcium during neuromuscular transmission. Hypermagnesemia is mostly iatrogenic like preeclampsia/eclampsia therapy. Serum magnesium levels are not always consistent with clinical course, so weakness should be carefully assessed.

Moreover iatrogenic MG has been defined with penicillamine, interferon therapy, and bone marrow transplantation. Symptoms are usually mild among these subjects, and MG is most often reversible with the discontinuation of the therapy, i.e., penicillamine and interferon. Onset after bone marrow transplantation varies between months to years. These patients require exceptional surgery.

Crisis is defined as a need for mechanical ventilation due to respiratory muscle weakness. In patients with MG, there is a risk of developing two kinds of crises with different therapeutic approaches: the myasthenic and the cholinergic crises. The myasthenic crisis is rather an exacerbation: It can be caused or provoked by factors like respiratory infections, emotional stress, and surgery. Specific immunotherapies (plasma exchange or intravenous immunoglobulin) are associated with a rapid recovery in few days in most of the cases [6]. A limited group of myasthenic crisis requires weeks to resolve with vigorous immunosuppressive therapy with underlying cause if it exists. Residual effects of long-lasting anesthetic drugs may also impair neuromuscular function in early postoperative course as in myasthenic crisis.

The cholinergic crisis may also appear with muscle weakness with even need for invasive mechanical ventilation. However, the main etiological factor is an overdose with cholinesterase inhibitors, and clinical presentation is with signs or symptoms associated (e.g., excessive salivation, sweating, abdominal cramps, urinary urgency, bradycardia, muscle fasciculation or weakness). Differential diagnosis may be problematic in some cases necessitating a single dose of edrophonium. This agent would improve symptoms in a myasthenic crisis, but they will worsen or not be changed in a cholinergic crisis.

The treatment consists of medical and surgical modalities. For an appropriate management of the perioperative period, it is useful to have some information also about the medical treatment of the patient, for it can be crucial in determining the optimal timing for the operation. The most important and common way of treatment is still symptomatic: Improving neuromuscular transmission is the key approach and achieved with an anti-AChE, mainly pyridostigmine [7, 11]. The drug results in increased ACh levels at neuromuscular junction as it decreases ACh degradation. The response to therapy may not be uniform for muscle groups [7].

Patients with anti-MuSK are less likely to respond pyridostigmine therapy [12]. In case of severe muscarinergic side effects, glycopyrronium bromide, atropine sulfate, and loperamide can be used.

Regarding the immunosuppressive therapy, corticosteroid therapy has been shown to be beneficial on slowing the progression [13]. Other alternatives for immunosuppressive therapy include azathioprine, cyclophosphamide, cyclosporine A, tacrolimus, and rituximab [6]. Patients under tacrolimus and cyclosporine therapy should be investigated preoperatively about renal impairment.

Plasma exchange and intravenous immunoglobulin are appropriate for myasthenic crisis or severe myasthenia [14]. However, both modalities can be performed prior to surgery to optimize neuromuscular function. Timing of surgery should be planned close to these aforementioned therapies in order to get the maximum benefit.

Myasthenic crisis is an emergency case and has to be treated under “intensive care” conditions with respiratory support, treatment of infections, and monitoring of vital functions and mobilization. Intravenous immunoglobulin (IVIG) and plasma exchange are options for further treatment; both can be given in sequence if necessary, as patients can respond to one but not to the other [15].

Treatment of cholinergic crisis includes endotracheal intubation, atropine, and cessation of cholinesterase inhibitors until the crisis is over.

Elective surgery for myasthenic patients should be reserved for a stable period of the disease when the medication requirement is minimal for uneventful perioperative course. It is mandatory – although not sufficient – to obtain neurological optimization in order to ensure an early and safe recovery in postoperative period. It should be kept on mind that vigilant preoperative assessment by an experimented anesthetist is the first step to reduce complications and need for ICU. Management with an experienced team would be rational to distinguish high-risk myasthenic patients and to diagnose and to treat acute postoperative complications. If acute cases with a high possibility of myasthenic crisis are presented, more aggressive strategies such as plasmapheresis or intravenous immunoglobulin can be necessary for the operative preparation [15].

Prediction of postoperative myasthenic crisis (POMC) would be very beneficial, both because of possible preventive approaches and also to plan a postoperative ICU admission. A recent article proposes a new predictive score of POMC (Table 8.3) [16]: Regarding this system, patients with a score of <2.5 have the probability of having a POMC of less than 10 %, while a score of >4.0 is associated with a POMC probability of approximately 50 %.