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Breach rhythm related to a solitary skull lesion caused by multiple myeloma

J van Doorn, P J Cherian

Department of Clinical Neurophysiology, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands

Correspondence to:
j.perumpillichira{at}erasmusmc.nl

An 83-year-old man with diabetes was admitted for excessive daytime sleepiness that began 2 weeks previously after he sustained a fall and concussion. He had a past history of multiple myeloma with a solitary skull lesion, requiring local radiotherapy. CT and MRI scans showed mild diffuse cerebral atrophy and the known skull lesion at the vertex (fig 1B, C). Blood biochemistry was normal. Psychiatric evaluation ruled out depression. EEG showed a focal increase in amplitude and frequency over the central midline, suggestive of breach rhythm (fig 1A). There were no epileptiform abnormalities on the EEG.

View this figure (60K): in this window | in a new window | PowerPoint for Teaching   Figure 1 (A) EEG shows sharp contoured activity of higher amplitude and faster frequency (breach rhythm) over the central midline (Cz) electrode. MRI T1 weighted sections (B, coronal, with gadolinium enhancement and C, sagittal) show the skull lesion with epidural and scalp extension.

 

Breach rhythm tends to develop over skull defects, mostly after cranial surgeries.¹ There is one previous report of this activity developing over an osteolytic skull metastasis.² Even though breach rhythm has a spiky morphology, it has no relationship to epilepsy.¹ However, the sharp contour of this rhythm makes it sometimes difficult to differentiate sporadic epileptiform abnormalities arising from the same region. In such a situation, recording a sleep EEG might help, if it shows attenuation or disappearance of the breach rhythm while the epileptiform abnormalities persist or increase. The mechanism underlying the development of this rhythm is unknown. In some patients, it may reflect enhancement of the underlying cerebral rhythm such as the mu rhythm, due to reduced electrical impedance over the bone defect. However, it may sometimes be better seen over an EEG electrode that is not directly overlying the skull defect.¹ Also, replacing the bone flap after cranial surgery has had a varied effect on this rhythm.¹ In many patients, the breach rhythm develops a few weeks or months after the surgery.¹ These suggest an underlying mechanism more complex than just the reduced filtering effect of the EEG signal caused by the absence of overlying bone. In our patient, investigations failed to reveal a cause for his excessive daytime sleepiness. Possibly this was due to postconcussion hypersomnia, related to his recent mild traumatic brain injury.³

This article has been adapted from van Doorn J, Cherian P J. Breach rhythm related to a solitary skull lesion caused by multiple myeloma Journal of Neurology, Neurosurgery and Psychiatry 2008;79:819

Competing interests: None.

Patient consent: Informed consent was obtained for publication of the case details in this report.

1. Cobb, WA, Guiloff, RJ, & Cast, J. Breach rhythm: the EEG related to skull defects. Electroencephalogr Clin Neurophysiol 1979;47:251–71.[CrossRef][Medline]
2. Radhakrishnan, K, Silbert, PL, & Klass, DW. Breach activity related to an osteolytic skull metastasis. Am J EEG Technol 1994;34:1–5.
3. Guilleminault, C, Yuen, K, Gulevich, MG, et al. Hypersomnia after head–neck trauma: A medicolegal dilemma. Neurology 2000;54:653–9.[Abstract/Free Full Text]

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