Ultrasound as Diagnostic Tool for Diaphragmatic Myoclonus

Abstract

Background

Diaphragmatic myoclonus is a rare disorder of repetitive diaphragmatic contractions, acknowledged to be a spectrum that includes psychogenic features. Electromyography has been the diagnostic tool most commonly used in the literature.

Methods

To test whether we could perform a noninvasive technique to delineate the diaphragm as the source of abnormal movements and demonstrate distractibility and entrainability, we used B‐mode ultrasound in a patient with diaphragmatic myoclonus.

Results

Ultrasound imaging clearly delineated the diaphragm as the source of her abdominal movements. We were able to demonstrate entrainability of the diaphragm to hand tapping to a prescribed rhythm set by the examiner.

Conclusions

We recommend the use of ultrasound as a noninvasive, convenient diagnostic tool for further studies of diaphragmatic myoclonus. We agree with previous findings that diaphragmatic myoclonus may be a functional movement disorder, as evidenced by distractibility and entrainability demonstrated on real‐time video with ultrasonography.

Diaphragmatic myoclonus is a rare disorder of repetitive contractions of the diaphragm. Previous reports with electromyography (EMG) demonstrated distractibility with hand tapping tasks, suggesting that the movements share mechanisms used also for volitional control.1

To test whether we could perform a noninvasive technique to delineate the diaphragm as the source of abnormal movements and demonstrate distractibility and entrainability, we used B‐mode ultrasound in a patient with diaphragmatic myoclonus.

Patients and Methods

We studied an 82‐year‐old woman, referred for sudden‐onset abdominal excursions after a stressful period, associated with anxiety and hyperventilation. Her abdominal excursions were severe enough to interfere with her balance, prompting cane use, but disappeared during sleep. She was examined by three movement disorders neurologists and found to have irregular, repetitive, distractible abdominal and chest wall excursions, consistent with diaphragmatic myoclonus. These movements appeared to entrain inconsistently, with noted poor effort on entrainment tasks. The patient had other psychogenic features on exam, such as developing new‐onset right‐leg tremor when presented to the senior attending physician.

We imaged the patient, using B‐mode ultrasound, lying supine at rest (Fig. 1) and with hand‐tapping tasks. We followed the technique similar to that used for ultrasound‐guided needle EMG of the diaphragm.2 We identified the 7th, 8th, and 9th ribs at the mid‐axillary line. The transducer was then placed perpendicular to the ribs, centered over the 8th intercostal space (ICS). After initial identification of the anatomy perpendicular to the long axis of the ribs, the transducer was rotated to orient it parallel to the ribs overlying the ICS. Real‐time imaging of structures within the 7th ICS was followed by scanning of the 7th and 9th ICS to identify the ICS that provided the best visualization of the diaphragm. Once optimal visualization of the diaphragm was achieved, we then proceeded with entrainment techniques, instructing the patient to tap her left hand following the examiner's hand‐tapping rhythm at her bedside. The examiner then varied tapping rhythm while recording real‐time imaging of the diaphragm (see Video 1). Videos for ultrasound and hand tapping were synchronized using a time stamp on the ultrasound machine and on the camera. The accuracy of the synchronization is to the nearest second.

Figure 1.

Ultrasound snapshot of the diaphragm and surrounding structures.

The National Institutes of Health CNS IRB approved the use of human subjects for this study. Written informed consent was obtained before to the start of the study.

Results

Ultrasound imaging clearly delineated the diaphragm as the source of her abdominal movements (Video 1). We were able to demonstrate distractibility and some entrainability of the diaphragm to hand tapping to a prescribed rhythm set by the examiner.

Discussion

Diaphragmatic myoclonus is puzzling, acknowledged to be a spectrum of disorders, with psychogenic features.1 Other names include diaphragmatic flutter, respiratory myoclonus, and Leeuwenhoek's disease (after the famed microscope inventor, Antony van Leeuwenhoek, who wrote an excellent description of his own ailment).3 Epigastric pulsation is the most common manifestation,4 disappearing in sleep,5, 6, 7 as in our patient. The majority have diaphragmatic contractions of 0.5 to 15 Hz, usually 2 to 5 Hz,5 characteristically irregular.7 Other common symptoms include dyspnea, hyperventilation, hiccups, or belching.5

Diaphragmatic myoclonus is well associated with postencephalitic illness, intrathoracic lesions,7 and cervical spine lesions. A tardive form, related to prochlorperazine, has also been reported.8 Phillips and Eldridge failed to reproduce EMG patterns in a healthy volunteer instructed to reproduce patient's movement disorder.9 However, Espay et al. used EMG to demonstrate, in 2 cases, that the movements were influenced by distracting tasks, such as hand tapping, Valsalva, or abdomen pressure.1 Kondo et al. showed, in 1 of 3 cases, that placebo‐controlled symptoms and abnormal contractions never occurred in 1 patient when electrophysiological recording was anticipated, suggesting that emotional states influenced movement attacks.6 The interpretation of the signs of distractibility and entrainability as being psychogenic are derived from skeletal muscles, and the diaphragm is different in that it has intrinsic involuntary control as well as voluntary control. One caveat is that the interpretation of the signs of distractibility and entrainability as being psychogenic are derived from skeletal muscles, and the diaphragm is different in that it has intrinsic involuntary control as well as voluntary control. This does raise caution given that it is theoretically possible for distraction and entrainment to influence an involuntary generator, but this physiology is not known.

Previous diagnostic tools used include fluoroscopy, phonocardiogram, strain gauge pneumogram, phrenic nerve interruption, and EMG.10 Surface EMG is imprecise, contaminated by chest wall musculature. Needle EMG of the diaphragm is invasive and uncomfortable. Ultrasound offers real‐time direct visualization, particularly useful because of the diaphragm's dynamic nature,2 and especially relevant as a noninvasive, painless diagnostic tool for diaphragmatic myoclonus. Accelerometry of the left‐hand tapping task may be used in future studies to more objectively quantify frequency and entrainment effort. Furthermore, we recognize that the time resolution of ultrasound is less than that for EMG, which remains more accurate for assessment of entrainment and coherence.

Reported successful treatments for diaphragmatic myoclonus include phenytoin, carbamazepine, haloperidol, and clonazepam; the latter was demonstrated to be highly effective and particularly chosen because of its success in other cases of segmental myoclonus.5

Conclusions

We recommend the use of ultrasound as a noninvasive, convenient diagnostic tool for further studies of diaphragmatic myoclonus. We agree with previous findings that diaphragmatic myoclonus may have features inconsistent with purely organic myoclonus syndromes, here demonstrated on real‐time video with ultrasonography.

Author Roles

(1) Research Project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript Preparation: A. Writing of the First Draft, B. Review and Critique.

V.F.M.L.R.: 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B

E.C.: 1A, 1B, 1C, 2A, 3A, 3B

B.I.K.: 1A, 1B, 2B, 2C, 3B

C.L.: 1A, 1B, 1C, 2A, 2B, 2C, 3B

K.A.: 1A, 1B, 1C, 2A, 2B, 2C, 3B

M.H.: 1A, 1B, 1C, 2A, 2B, 2C, 3B

Disclosures

Funding Sources and Conflicts of Interest: The study was supported by the National Institute of Neurological Disorders and Stroke Intramural Program. The authors acknowledge that this manuscript was prepared as part of their official duties as employees of the Department of Health and Human Services (DHHS). Work presented here does not officially express the opinion of DHHS.

Financial Disclosures for previous 12 months: Dr. Ramos is a federal government employee, working for the National Institutes of Health (NIH). This work was undertaken as part of her official duty. Her research at the NIH is supported by the NIH Intramural Program. Elaine Considine, RN, is a federal government employee, working for the NIH. This work was undertaken as part of her official duty. Her research at the NIH is supported by the NIH Intramural Program. Dr. Karp is a federal government employee, working for the National Institutes of Health. This work was undertaken as part of her official duty. Her research at the NIH is supported by the NIH Intramural Program. Dr. Karp is an investigator on a study that receives research support from Allergan through a Clinical Trials Agreement (CTA) with the NIH. Dr. Lungu is a federal government employee, working for the NIH. This work was undertaken as part of his official duty. Dr. Lungu's research at the NIH is supported by the NIH Intramural Program. Dr. Alter is an employee of Mount Washington Pediatric Hospital and a federal government contractor, working for the NIH. This work was undertaken as part of her official duty at NIH. She has received consulting honoraria from Allergan and speaking honoraria from Ipsen. She has received royalties from Demos Medical Publishing. Dr. Hallett is a federal government employee, working for the NIH. This work was undertaken as part of his official duty. Dr. Hallett's research at the NIH is largely supported by the NIH Intramural Program. Dr. Hallett serves as chair of the medical advisory board for and receives honoraria and funding for travel from the Neurotoxin Institute. He may accrue revenue on US Patent #6,780,413 B2 (Issued: August 24, 2004): Immunotoxin (MAB‐Ricin) for the treatment of focal movement disorders, and US Patent #7,407,478 (Issued: August 5, 2008): Coil for Magnetic Stimulation and methods for using the same (H‐coil); in relation to the latter, he has received license fee payments from the NIH (from Brainsway) for licensing of this patent. He is on the editorial board of 22 journals, and received royalties from publishing from Cambridge University Press, Oxford University Press, John Wiley & Sons, Wolters Kluwer, and Elsevier. He has received honoraria for lecturing from Columbia. Supplemental research funds came from the Kinetics Foundation, for studies of instrumental methods to monitor Parkinson's disease, BCN Peptides, S.A., for treatment studies of blepharospasm, and Medtronics, Inc., for studies of DBS, through a CTA with the NIH.

Supporting information

A video accompanying this article is available in the supporting information here.

Video 1. Intermittent chest and abdominal movements with vocalizations in an 82‐year‐old female. Ultrasound imaging delineated diaphragm as the source of intermittent movements and demonstrated entrainability of the diaphragm to left‐hand tapping to a prescribed rhythm set by the examiner.