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A Woman in Her 70s With a History of Myasthenia Gravis Complains of Shortness of Breath FREE TO VIEW

Craig Fryman, MD; Sahar Ahmad, MD
Author and Funding Information

aDepartment of Internal Medicine, Stony Brook University, Stony Brook, NY

bDivision of Pulmonary and Critical Care Medicine, Stony Brook University, Stony Brook, NY

CORRESPONDENCE TO: Craig Fryman, MD, 101 Nicolls Rd, Health Sciences Center T16, Room 020, Stony Brook, NY 11794-8410


Copyright 2017, American College of Chest Physicians. All Rights Reserved.


Chest. 2017;151(4):e73-e76. doi:10.1016/j.chest.2016.07.051
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Published online

A woman in her 70s with myasthenia gravis (MG) and a history of myasthenia crisis presented with progressively worsening dyspnea for 3 days. Associated symptoms included chronic diplopia and lower extremity weakness. She denied any slurred speech or dysphagia.

She was afebrile and hemodynamically stable with a respiratory rate of 24 breaths/min and a pulse oximetry of 98% on room air. She appeared anxious. Physical examination demonstrated right eye ptosis and decreased breath sounds over the right lower posterior lung field. Her chest radiograph is shown in Figure 1.

Figure Jump LinkFigure 1 Chest radiograph demonstrating a small right pleural effusion.Grahic Jump Location

Her vital capacity (VC) and negative inspiratory force (NIF) were markedly low at 104 mL and –30 cm H2O, respectively. Her VC and NIF were reevaluated 1 h later and remained low at 112 mL and –35 cm H2O, prompting a medical ICU consultation for impending respiratory failure. The ICU consultant performed a focused, goal-directed ultrasound to evaluate the patient’s diaphragm position and function to help guide management and determine a need for mechanical ventilation (Figs 2, 3, Video 1).

Figure Jump LinkFigure 2 Diaphragm thickness at end-inspiration with a linear-array transducer probe.Grahic Jump Location

Figure Jump LinkFigure 3 Diaphragm thickness at end-expiration with a linear-array transducer probe.Grahic Jump Location

Question: Based on the clinical history and imaging studies, is this patient in myasthenia crisis?

Answer: Based on our findings of normal diaphragmatic excursion and a thickening fraction within the normal range, myasthenia crisis was considered unlikely. According to the additional chest ultrasound findings in clinical context, the source of the patient’s dyspnea was attributed to the presence of pulmonary edema.

This patient presented with dyspnea and exhibited low VC and NIF on two measurements. A focused bedside ultrasound examination was performed to assess whether symptoms were a consequence of diaphragm dysfunction and to determine to what extent patient effort and technique contributed to the abnormal bedside VC and NIF values (Discussion Video).

A global view of the diaphragm was initially obtained to assess for any structural or functional abnormalities. Video 1 demonstrates a global view of the diaphragm and its surrounding structures. The diaphragm is displayed as a thin hyperechoic structure cephalad to and abutting the liver. An anechoic fluid collection is abnormally present between the diaphragm and lung. Normal direction of diaphragm excursion is noted, as the diaphragm is observed moving caudad when the patient is instructed to inspire. An absence of excursion or the presence of paradoxical motion, in which the diaphragm moves cephalad during inspiration, indicates significant dysfunction; this finding is consistent with but not limited to myasthenia crisis.

Measurement of diaphragm thickness (Tdi) has proven accurate with the use of ultrasound and has been used in several studies evaluating a variety of populations, including healthy volunteers and patients with suspected diaphragm dysfunction., Assessment of the relative changes in Tdi that occur throughout a respiratory cycle, represented by the thickening fraction (TF), has been used as a measure of diaphragm function. Measurement of diaphragm thickening has been shown to correlate with maximal inspiratory pressure in normal and elderly adults. It has also shown good performance in predicting successful extubation during spontaneous breathing or pressure support trials. The TF is calculated as follows: (Tdi inspiration – Tdi expiration)/Tdi expiration. A change in Tdi of 28% to 96% has been reported in healthy volunteers and a change of < 5% in those with a paralyzed diaphragm.

Tdi was measured by using a high-frequency linear-array transducer probe. The right hemidiaphragm was visualized in B-mode at the zone of apposition, the area where the diaphragm abuts the rib cage, at a right anterior to mid-axillary scan plane between the eighth and 10th intercostal spaces. Figures 2 and 3 demonstrate Tdi at end-inspiration and end-expiration, respectively. Each image contains an aggregate of three horizontal stripes. These stripes (from near-screen to far-screen) represent the parietal layer, continuous with the parietal layer of the lung pleura; the muscular layer of the diaphragm itself; and the peritoneal layer, continuous with the abdominal peritoneum. Tdi inspiration and expiration were 0.44 cm and 0.30 cm, respectively, which corresponds to a TF of 0.47.

Although the patient initially appeared stable, the low VC and NIF were highly concerning, particularly given a history of crisis. The diaphragm TF of 47%, however, which is a value well above the lower limit of what is accepted as compatible with successful independent respiration, suggested that a bedside lung function study might not have been a reliable indicator in this particular scenario. VC and NIF are highly effort- and technique-dependent measurements. Accuracy of measurements in the setting of neuromuscular disease, in particular, may be affected by several factors, including difficulties coordinating movement as well as the inability to produce an adequate mouth seal around the device.

Using bedside ultrasound, we were able to rule out diaphragm dysfunction due to myasthenia crisis. Until we demonstrated normal diaphragm function by ultrasound, this finding was the presumed diagnosis given the patient's history. Further ultrasound investigation revealed a B-line-predominant pattern and small pleural effusions, which suggested pulmonary edema. The patient was ultimately admitted to the medicine floors and experienced symptom improvement with diuresis. In summary, this case comprised respiratory failure at which point-of-care ultrasound was used to rule out a specific diagnosis and to evaluate for alternative etiologies.

To our knowledge, there are no publications presently available that specifically address the utilization of diaphragm ultrasonography in the evaluation of patients with MG or suspected myasthenia crisis. Our case illustrates the potential for further research directed toward implementing this imaging modality for this condition.

Bedside ultrasound facilitates a noninvasive, nonionizing, and cost-effective means of examining the diaphragm in a dynamic setting, making it a preferred tool compared with other widely used imaging modalities. We posit that insight into diaphragm behavior in patients with MG who present with suspected myasthenia crisis could aid the physician in guiding therapy and determining patient disposition. In our case, an unnecessary initiation of mechanical ventilation and treatment for myasthenia crisis were avoided with the use of goal-directed ultrasound.

  • 1.

    Use of bedside spirometry and NIF measurement are a mainstay in the evaluation of patients who present with suspected myasthenia crisis; however, spirometry and NIF measurement may not always be reliable due to patient effort or the technique by which the test is performed.

  • 2.

    Diaphragm function can be quickly and easily assessed with the use of bedside ultrasound.

  • 3.

    Evaluation of the diaphragm and its function in a patient with suspected myasthenia crisis provides useful, reliable, and objective information that can aid the treating physician in guiding therapy.

Financial/nonfinancial disclosures: None declared.

Other contributions:CHEST worked with the authors to ensure that the Journal policies on patient consent to report information were met. The authors thank Sean Cavanaugh, BS, and Michael Boucher, EMT-P, for help with video production.

Additional information: To analyze this case with the videos, see the online version of this article.

Cohn D. .Benditt J.O. .Eveloff S. .McCool F.D. . Diaphragm thickening during inspiration. J Appl Physiol (1985). 1997;83:291-296 [PubMed]journal. [PubMed]
 
Ueki J. .De Bruin P.F. .Pride N.B. . In vivo assessment of diaphragm contraction by ultrasound in normal subjects. Thorax. 1995;50:1157-1161 [PubMed]journal. [CrossRef] [PubMed]
 
Gottesman E. .McCool F.D. . Ultrasound evaluation of the paralyzed diaphragm. Am J Respir Crit Care Med. 1997;155:1570-1574 [PubMed]journal. [CrossRef] [PubMed]
 
Grosu H.B. .Lee Y.I. .Lee J. .Eden E. .Eikermann M. .Rose K.M. . Diaphragm muscle thinning in patients who are mechanically ventilated. Chest. 2012;142:1455-1460 [PubMed]journal. [CrossRef] [PubMed]
 
Boon A.J. .Harper C.J. .Ghahfarokhi L.S. .Strommen J.A. .Watson J.C. .Sorenson E.J. . Two-dimensional ultrasound imaging of the diaphragm: quantitative values in normal subjects. Muscle Nerve. 2013;47:884-889 [PubMed]journal. [CrossRef] [PubMed]
 
Summerhill E.M. .Angov N. .Garber C. .McCool F.D. . Respiratory muscle strength in the physically active elderly. Lung. 2007;185:315-320 [PubMed]journal. [CrossRef] [PubMed]
 
DiNino E. .Gartman E.J. .Sethi J.M. .McCool F.D. . Diaphragm ultrasound as a predictor of successful extubation from mechanical ventilation. Thorax. 2014;69:423-427 [PubMed]journal. [PubMed]
 

Figures

Figure Jump LinkFigure 1 Chest radiograph demonstrating a small right pleural effusion.Grahic Jump Location
Figure Jump LinkFigure 2 Diaphragm thickness at end-inspiration with a linear-array transducer probe.Grahic Jump Location
Figure Jump LinkFigure 3 Diaphragm thickness at end-expiration with a linear-array transducer probe.Grahic Jump Location

Tables

References

Cohn D. .Benditt J.O. .Eveloff S. .McCool F.D. . Diaphragm thickening during inspiration. J Appl Physiol (1985). 1997;83:291-296 [PubMed]journal. [PubMed]
 
Ueki J. .De Bruin P.F. .Pride N.B. . In vivo assessment of diaphragm contraction by ultrasound in normal subjects. Thorax. 1995;50:1157-1161 [PubMed]journal. [CrossRef] [PubMed]
 
Gottesman E. .McCool F.D. . Ultrasound evaluation of the paralyzed diaphragm. Am J Respir Crit Care Med. 1997;155:1570-1574 [PubMed]journal. [CrossRef] [PubMed]
 
Grosu H.B. .Lee Y.I. .Lee J. .Eden E. .Eikermann M. .Rose K.M. . Diaphragm muscle thinning in patients who are mechanically ventilated. Chest. 2012;142:1455-1460 [PubMed]journal. [CrossRef] [PubMed]
 
Boon A.J. .Harper C.J. .Ghahfarokhi L.S. .Strommen J.A. .Watson J.C. .Sorenson E.J. . Two-dimensional ultrasound imaging of the diaphragm: quantitative values in normal subjects. Muscle Nerve. 2013;47:884-889 [PubMed]journal. [CrossRef] [PubMed]
 
Summerhill E.M. .Angov N. .Garber C. .McCool F.D. . Respiratory muscle strength in the physically active elderly. Lung. 2007;185:315-320 [PubMed]journal. [CrossRef] [PubMed]
 
DiNino E. .Gartman E.J. .Sethi J.M. .McCool F.D. . Diaphragm ultrasound as a predictor of successful extubation from mechanical ventilation. Thorax. 2014;69:423-427 [PubMed]journal. [PubMed]
 
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