Clinical Pathology: Transfusion Medicine

• Myasthenia gravis is an autoimmune disease most commonly caused by antibodies against the acetylcholine receptor (anti-AChR) on the muscle cell motor endplate at the neuromuscular junction. The acetylcholine receptors on the muscle are then unresponsive to impulses sent by presynaptic nerves, leading to weakness and fatigue in skeletal muscles.

• Anti-AChR antibodies are detectable in 80% to 90% of patients. These antibodies can block impulses sent by afferent nerves, decrease the number of available receptors at the motor endplate, or lead to cellular damage.

• Antibodies against the muscle-specific receptor tyrosine kinase (anti-MusK) are found in approximately 50% of patients without identifiable anti-AChR antibodies.

• Myasthenia gravis may be treated with cholinesterase inhibitors, immunosuppressive medications, therapeutic plasma exchange (TPE), and intravenous gamma globulin (IVIg).

• There is an increased incidence of thymomas in patients with myasthenia gravis. Thymectomy can produce disease remission or improvement in patients both with and without thymomas.

• Myasthenia gravis (moderate and severe) and prethymectomy are category I indications for using TPE according to the American Society for Apheresis (ASFA) guidelines published in 2013.

• TPE should consist of 1 to 1.5 total plasma volumes using albumin, with or without saline, as replacement fluid.