Reply

Donald L. Bliwise, PhD, David B. Rye, MD, PhD,and Lynn Marie Trotti, MD

We thank Drs Postuma and Gagnon for their comments and

the opportunity to present additional data. Determination of

relative symmetry was made by clinical exam. We stated previ-

ously in the paper1 (see Table heading and Figure caption) that

40 cases had predominantly asymmetric presentation, not that

such patients had ‘‘only unilateral impairment.’’ We agree

entirely that with average disease duration approaching 10

years, it would be unusual to find involvement of a single body

side. Because 28 patients had full Unified Parkinson Disease

Rating Scale (UPDRS), we have now examined those cases in

greater detail to provide the magnitude of the relative asymme-

try. We computed the difference between the maximally

affected and less affected side by summing the individual items

on the UPDRS for resting tremor, action tremor, rigidity,

open/close hand movements, rapid alternating hand move-

ments, and foot agility. For this smaller subset of patients, the

affected minus unaffected side difference for predominantly

asymmetric patients (n ¼ 23; X ¼ 3.3 [2.9]) tended to be

higher when compared to that for patients classified clinically

as symmetric (n ¼ 5; X ¼ 2.2 [0.8]), but did not reach statisti-

cal significance (t ¼ 1.64, p ¼ 0.11). We also compared phasic

electromyogram metric (PEM) rates between these subgroups

and found that even with Bonferroni adjustment, PEM rates

during rapid eye movement (REM) sleep in left brachioradialis

continued to be significantly higher in symmetric patients (38.9

[20.5] vs 16.6 [11.5], t ¼ 3.11, p ¼ 0.005). With regard to

association between symmetry and REM sleep behavior disorder

history, the occurrence was not significantly different in sym-

metric versus predominantly asymmetric patients (27.3% vs

45.5%, chi-square ¼ 1.23, p ¼ 0.29).

Finally, we were very encouraged by Drs Postuma and

Gagnon’s similar findings regarding greater rates of tonic REM

activity in the mentalis of symmetric patients. Tonic electro-

myographic (EMG) activity recorded with surface electrodes is

an amalgam of individual motor units firing under varying

properties of tension and stretch,2 but convergent/discriminant

validity for the differentiation of tonic and phasic EMG read-

ings from surface electrodes has never been demonstrated by

any research team. Given that phasic EMG has been quanti-

fied in human sleep successfully for >40 years,3,4 and that

twitching is widespread in distal flexors (toe, finger) during

sleep3,5 and is prominent in rat vibrissae,6 we are inclined to

view such activity as far more elemental and amenable to

quantification.

Potential Conflicts of Interest

DBR is on the Advisory Board for GSK, Boehringer Ingelheim,

Jazz Pharmaceuticals, Cephalon, Johnson & Johnson and is a

consultant for UCB, GSK decode genetics.

Department of Neurology, Emory University School of Medicine,Atlanta, GA

References

1. Bliwise DL, Trotti LM, Greer SA, et al. Phasic muscle activity insleep and clinical features of Parkinson disease. Ann Neurol 2010;68:353–359.

2. Bliwise DL, He L, Ansari FP, Rye DB. Quantification of electromyo-graphic activity during sleep: a phasic electromyographic metric.J Clin Neurophysiol 2006;23:59–67.

3. Stoyva JM. Finger electromyographic activity during sleep: itsrelation to dreaming in deaf and normal subjects. J Abnorm Psy-chol 1965;70:343–349.

4. Nakazawa Y, Kotorii T, Ohshima M, Kitahara T. Phasic muscular activityand muscular tonus in REM sleep. KurumeMed J 1973;20:105–112.

5. Morrish E, King MA, Pilsworth SN, et al. Periodic limb movementin a community population detected by a new actigraphy tech-nique. Sleep Med 2002;3:489–495.

6. Lerma J, Garcia-Austt E. Hippocampal theta rhythm during para-doxical sleep. Effects of afferent stimuli and phase relationshipswith phasic events. Electroencephalogr Clin Neurophysiol 1985;60:46–54.

DOI: 10.1002/ana.22396

906 Volume 69, No. 5