Myasthenia Gravis
Answer: C
Myasthenia gravis (MG) has two major presentations in the Emergency Department. The first is undiagnosed MG presenting with generalized weakness, bulbar symptoms, and/or respiratory signs or symptoms. The differential diagnosis for this presentation is vast and beyond the scope of this discussion; however, a new diagnosis of MG belongs in our thought process in the evaluation of the newly weak patient.
More commonly, EPs are faced with the evaluation and management of those with known MG. Since many early warning signals are symptoms that overlap with may serious or benign conditions (fatigue, subjective weakness, anxiety over symptoms), it is not uncommon to underestimate a MG patient’s presenting symptoms without objective findings. Myasthenic crisis is a serious sequela that occurs in 27% of those affected with MG. Before better evaluation and management, the mortality rate in the 1960s was as high as 42%; today, with better understanding, evaluative measures, and treatment, the mortality rate has declined to 5%.
Common presenting signs or symptoms of myasthenic crisis are ptosis, diplopia, facial weakness, dysarthria, dysphagia, and fatigable proximal (sometimes distal) limb weakness (at times weakness may not be symmetrical, prompting an evaluation for stroke). Early and repeated objective measures of the patient’s respiratory status are crucial. Negative inspiratory force (NIF) should be documented and trended; a NIF of -20 cmH20 or less is an indication for endotracheal intubation. Placing a patient on NIPPV may be an option in those with a diminished but not dangerously weak respiratory apparatus. Our patient is respiring comfortably now; NIPPV without further investigation is premature (A).
The differential diagnosis is still broad in this case, and a diagnosis of pulmonary embolism may be considered. However, CT with contrast (B) must be judiciously considered, as the iodinated contrast agent can precipitate a crisis. Further history and physical examination will guide the physician in his pretest probability and urgency for the study.
Sometime simply getting a better sense of what has been happening with our patients can elucidate the clinical context. What may seem to be a mundane office visit may reveal important information, such as that the patient has been taking ciprofloxacin, a fluroquinolone, whose drug class is well known to worsen MG or precipitate a crisis (other drugs include magnesium sulfate, β-Blockers, calcium channel blockers, and aminoglycosides). Without this historical piece of information (C), this patient’s unclear and potentially worrisome clinical trajectory may be underrecognized, and she may prematurely (and unsafely) go home with a non-diagnosis (D).
In the ED, we are charged with the confirmation of diagnosis (known or suspected), evaluation of respiratory status, initiating or facilitating immunomodulatory treatment (IVIg and/or plasmapharesis), and managing and/or avoiding complications, such as respiratory failure/terminal fatigue.
Our patient is at risk for deterioration, given symptoms in the context of an aggravating agent (ciprofloxacin); her NIF was -30 to -40 cmH20 on serial assessments, was admitted to the ICU for close monitoring, and did well with 2g/kg IVIg administered over 3 days.
Reference
Lacomis D. Myasthenic crisis. Neurocrit Care. 2005;03:189–194.