Comparative effects of plasma exchange and pyridostigmine on respiratory muscle strength and breathing pattern in patients with myasthenia gravis.

Abstract

Background-Pyridostigmine, an acetylcholinesterase antagonist, is useful in improving respiratory function in patients with myasthenia gravis. More recently, plasma exchange has been employed in myasthenia gravis because it acts presumably by removal of circulating antibodies against acetylcholine receptors. Surprisingly, comparative data on the effects of pyridostigmine and plasma exchange on lung volumes, respiratory muscle strength, and ventilatory control system in patients with myasthenia gravis are lacking. Methods -Nine consecutive patients with grade Ilb myasthenia gravis were studied under control conditions and after a therapeutic dose of pyridostigmine. In a second study the patients were re-evaluated a few days after a cycle of plasma exchange, before taking pyridostigmine. In each subject pulmonary volumes, inspiratory (MIP) and expiratory (MEP) muscle force, and respiratory muscle strength, calculated as average MIP and MEP as percentages of their predicted values, were measured. The ventilatory control system was evaluated in terms of volume (tidal volume, VT) and time (inspiratory time, TI, and total time, TTOT) components of the respiratory cycle. Mean inspiratory flow (VT/TI) -that is, the "driving" -and TI/TToT -that is, the "timing" -components ofventilation were also measured.Results -In each patient treatment relieved weakness and tiredness, and dyspnoea grade was reduced with plasma exchange. Following treatment, vital capacity (VC) increased on average by 9-7% with pyridostigmiine and by 14% with plasma exchange, and MIP increased by 18% and 26%, respectively. In addition, with plasma exchange but not with pyridostigmine forced expiratory volume in one second (FEV1) increased by 16% and MEP increased by 24-5%, while functional residual capacity (FRC) decreased a little (6-8%). The change in respiratory muscle strength was related to change in VC (r2 = 0.48). With plasma exchange, VT increased by 18*6% and VT/TI increased by 13-5%, while neither TI nor TIrrTOT changed.Conclusions -Plasma exchange can be used in patients with myasthenia gravis when symptoms are not adequately controlled by anticholinesterase agents. Plasma exchange increases respiratory muscle force and tidal volume due to changes in "driving" but not "timing" of the respiratory cycle.

Evidence-based guideline update: Plasmapheresis in neurologic disorders [RETIRED]

“…This study found improvement in respiratory measures, including a decrease in functional residual capacity and residual volume and an increase in forced expiratory volume in 1 second, maximum inspiratory pressure, and maximum expiratory pressure ( p Ͻ 0.05) in the plasmapheresis cohort. 16 A retrospective Class III study compared 19 patients treated with a single session of plasmapheresis prior to thymectomy vs 32 patients treated with thymectomy alone. The patients treated with plasmapheresis had less occurrence of crisis in the following month ( p ϭ 0.0724) and year ( p ϭ 0.049) and a greater remission rate at 5-7 years postoperatively.…”

Predictable recovery from myasthenia gravis crisis with plasma exchange: Thirty-six cases and review of current management

“…A useful study from Florence compared improvement in breathing pattern (vital capacity) in MG by treatment by pyridostigmine (VC +10%) vs. PEX (VC +14%) and MIP (Mean inspiratory pressure) increases of 18 and 26%, respectively [60]. A French report of failure to wean from a respirator a typical MG patient under 2 years CS treatment with 4 PEX and Azathioprine showed steroid-induced myopathy by histology along with peripheral and diaphragm EMG [61].…”

Pitfalls in the Ventilator Management of Myasthenia Gravis: Autonomic Instability and Anticholinesterase-Induced Airway Resistance

“…Use of plasmapheresis in the treatment modality of MG was reported as early as 1976 by pinching et al, 5 Plasmapheresis is known to improve respiratory function when compared with pyridostigmine and is found to be useful in ventilator dependency in a non randomized trial of nine patients. 6 The use of plasmapheresis to control MC or in preoperative preparation of thymectomy remains inadequately studied. 7 In our case clinical course was complicated by autonomic instability, a rare but recognized manifestation of MG.…”