PMC8311021_01
Surface EMG findings. A surface EMG (A-D) was recorded on day 4 under continuous infusion of midazolam (0.1 mg/kg/h) and propofol (1.0 mg/kg/h). Panel (A) shows the continuous simultaneous co-contraction of agonist and antagonist muscles at rest. Panel (B) shows ~9 Hz rhythmic bilaterally synchronous brief muscle contractions in the lower limbs (manifesting as periodic myoclonic jerks). Panels (C,D) show two spreading patterns descending from the facial muscles (C) or ascending from the leg muscles (D). Myoclonic jerks were also triggered by sudden sound or touch (not shown). Another surface EMG was recorded on day 60, during a continuous infusion of dexmedetomidine (0.45 mug/kg/h) (E) and 90 min after discontinuation of the dexmedetomidine (F) to explore the inhibitory effect of dexmedetomidine on hyperexcitability of the alpha motoneurons to the jaw jerk reflex maneuver. Panel (E) shows that the tapping of the lower jaw (arrowheads) triggers muscle contraction limited to the SCM and OO, but panel (F) shows muscle contractions propagating into the TA. In panels (A,C-F), a surface EMG was obtained from the left-sided muscles. BF, biceps femoris; ECU, extensor carpi ulnaris; EMG, electromyogram; FCU, flexor carpi ulnaris; GC, gastrocnemius; OO, orbicularis oculi; RA, rectus abdominis; SCM, sternocleidomastoid; TA, tibialis anterior.
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F1
A surface EMG examination obtained on day 4 showed simultaneous agonist-antagonist continuous muscle activity (Figure 1) compatible with a diagnosis of SPSD. Bilaterally synchronized periodic myoclonic jerks in his lower limbs were also observed (Figure 1). The potential inhibitory effect of dexmedetomidine on the propagation of hyperekplexia was confirmed by surface EMG (Figure 1).
Clinical course of clusters of myoclonic jerks and paroxysmal sympathetic hyperactivity. Despite continuous infusion of midazolam and propofol, the patient frequently developed severe clusters of myoclonic jerks and PSH. The patient was also treated with a 5-day course of IVMP from day 2, and IVIg from day 8 of admission, but the clusters did not respond to the GABAergic agents and immunotherapy. However, the frequency of the clusters rapidly declined after dexmedetomidine treatment, which was started from day 9 of admission. After that, the episodic symptoms were controlled during the remainder of his hospitalization (see text). IVIg, intravenous immunoglobulin; IVMP, intravenous high-dose methylprednisolone; PSH, paroxysmal sympathetic hyperactivity.
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F2
Surprisingly, after commencing dexmedetomidine, the clusters of myoclonic jerks with PSH rapidly ameliorated, without any remarkable adverse events (Figure 2).