myasthenia gravis ( mg ) is an autoimmune disorder resulting from the production of antibodies against acetylcholine receptors leading to the destruction of the postsynaptic membrane at the neuromuscular junction , which results in variable muscle weakness made worse by exercise . however , most of the patients who develop respiratory symptoms do so during the late course of disease and already have other neurological signs and symptoms . we present a case of previously undiagnosed mg who presented with recurrent acute respiratory failure . she also denied symptoms of upper and lower extremity weakness , blurred vision , or swallowing difficulty . further history revealed that she had speech problem ( nasal speech ) treated by ent surgeons and speech therapist . on the physical examination , she had labored breathing with respiratory rate of 40 breaths / minute . the blood pressure was 146/98 mm hg , pulse was 104/minute and regular and body temperature was 36.7c . the arterial blood gas analysis on an o2 mask with 10 l was ph7.314 , paco2 56.7 mm hg , pao2 92.2 mmhg and oxygen saturation 90% . the chest x - ray revealed no definite infiltration but the lung volume was reduced . other laboratory evaluation showed a white blood cell count of 6980 l , hemoglobin of 12.5 g / dl and platelet count of 345 000 l , blood glucose 94 mg / dl , bun / cr 12/0.8 mg / dl , ast / alt the chest computed tomography ( ct ) scan showed no definite evidence of pulmonary thromboembolism . as respiratory failure was imminent , she was promptly given supplemental oxygen and transferred to the intensive care unit and mechanically ventilated under rapid sequence induction ( iv midazolam 3 mg and succinylcholine 70 mg ) . however , she was unable to breathe without mechanical support even after the effect of muscle relaxant had worn off . we considered other causes of respiratory failure such as neuromuscular disorders , guillain  barre syndrome or mg . her condition gradually improved with pyridostigmine bromide 720 mg / day and prednisolone 30 mg / day and intravenous gamma - globulin 400 mg / kg /day for 5 days were administered . weaning from ventilator failed over the next 2 weeks ; therefore , a tracheostomy was performed . however , the patient was eventually successfully weaned from the ventilator and 2 months later , she was discharged . she was advised to do thymectomy but she developed again respiratory distress and subsequent respiratory arrest with signs and symptoms of sepsis . the prednisolone and pyridostigmine were stepped up along with antibiotics , fluid , and intravenous gamma - globulin 400 mg / kg / day for 5 days she received . currently she was still followed up in our hospital and responded well with maintenance steroid and pyridostigmine . respiratory failure can be a complication during the late course of mg in about 3% to 8% of cases , known as a mysthenic crisis . however , isolated respiratory failure as the presenting symptom , as in the present case , is very unusual and this patient in our knowledge is the first case reported in the literature . our case has demonstrated the rare but well - known manifestation of mg . indeed our patient has already presented with symptoms of dysphonia for 3 months to ent department , which was compatible with mg . as the diagnosis was not known at our department , succinylcholine was used as muscle relaxant for rapid sequence intubation . we did not find any evidence of a hypoxemic respiratory failure ; there were no definite infiltrations , edema , effusion , or pneumothorax on chest x - ray . there was no evidence of pulmonary thromboembolism on chest ct scan and no evidence of intracardiac shunting or congestive cardiac failure on echocardiography . based on these results , we investigated the possibility of a neuromuscular disease , especially the guillian barre syndrome and mg , the most common and the second most common cause of neuromuscular disease , respectively . however , the cerebrospinal fluid was normal , and the neurophysiological studies showed evidence of mg . they may present with stridor.[68 ] the vocal cords of our patient was also involved by the disease as she already had a speech problem . generally patients with neuromuscular disease present with hypoxia and a normal d ( a - a ) o2 due to hypoventilation , but in the present patient there was an increased d(a - a)o2 . patients with mg occasionally have atelectasis which could result in this finding . it is difficult to consider a neuro muscular disorder , especially mg , unless there are other neurological symptoms such as ocular or bulbar symptoms . myasthenic cases with positive anti - musk antibody tend to be young female subjects presenting with bulbar weakness , and often responding poorly to symptomatic treatment with a higher risk of respiratory failure . an obvious advantage of plasmapheresis over high doses of intravenous immunoglobulins has not been demonstrated ; however , rapid effects of plasmapheresis support this therapeutic approach . our patient presented only with respiratory symptoms , the patient had no other symptoms , generally associated with mg during her 6-month follow up visits . patients , on occasions , may present to the emergency department because of acute exacerbation . though most of them were known cases , we should be aware of some unrecognized cases and should consider mg as a differential diagnosis for patient with acute respiratory failure .
acute respiratory failure is an uncommon initial presentation of myasthenia gravis ( mg ) . in our case a 22-year - old woman of unrecognized mg presented to the emergency department with isolated respiratory failure as the first presenting symptom . 
 initially she presented with dysphonia and was managed by speech therapist and ent surgeons for 3 months . 
 subsequently , she presented with signs and symptoms of sepsis and went into acute respiratory failure . 
 this case highlights the need to consider mg in the differential diagnosis of an otherwise unexplained respiratory failure in the critical care setting .