Mittens

Description

This pattern’s name is a description of its appearance as the outline of a mitten. The outline is produced through the partial superimposition of a sharp wave on the up slope of a following slow wave of the same polarity. The overlap produces a notching in the slow wave that divides the slow wave into two compartments, which are a smaller and sharper thumb compartment, and then a larger and rounder hand compartment (Erwin et al., 1984). Mittens occur as individual waves that are centered in the frontal-central midline with extension into the parasagittal regions bilaterally and possible inclusion of the parietal region also. The duration usually is about 400 to 500 milliseconds and the amplitude is high and equivalent to that of the surrounding delta frequency range activity. The pattern emerges out of anterior, polymorphic delta activity of deep sleep. Montages with long interelectrode distances, such as an ipsilateral ear reference montage, depict mittens most clearly. Mittens are typically found in adults and rarely occur before the age of 15 years (Gibbs and Gibbs, 1964).

Distinguishing Features

• Compared to K Complexes

Similar to K complexes, mittens are individual complexes that occur at the midline during non–rapid eye movement (NREM) sleep; however, mittens differ in waveform polarity. The two major component elements of a mitten have the same polarity, and the major elements of K complexes are two sharp waves of opposite polarity. The localization also can be helpful in differentiating because mittens typically are centered anterior to the vertex and K complexes are at the vertex.

• Compared to Interictal Epileptiform Discharges

The pairing of a sharp wave and a slow wave gives mittens a description that resembles bifrontal or generalized interictal epileptiform discharges (IEDs), but mittens’ waveform differs considerably from IEDs’. The sharp wave element of a mitten has a longer duration and a less sharp contour than the initiating sharp wave of an IED. The inconsistency in the temporal relationship between the two component waves of a mitten also distinguishes it from an IED. For each individual patient, the sharp wave and the slow wave of the IEDs have a relatively fixed temporal relationship. The initiating sharp wave always occurs at the same distance from the slow wave’s peak.

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