Tremor after long term lithium treatment; is it cortical myoclonus?

Table 1 Electroclinical and neuroimaging findings

Case no	Age at onset (Gender)	Years on lithium	Gluten sensitivity	Cerebellar MRS	JLA & CC^c	SEPs	Postural tremor^e frequency	Psychotropic medication daily doses
1	77y, F	40y	–	Reduced NAA/Cr ^a vermis 0.91 hemispheres 0.78	Action and stimulus reflex cortical myoclonus	“Giant” & C-reflexes ^b	14 Hz	Lithium ^d 400 mg Mirtazapine 45 mg
2	63y, F	10y	+ IgG	Reduced NAA/Cr vermis 0.87 hemispheres 1.04	Cortical myoclonus	normal	10 Hz	Lithium 400 mg Mirtazapine 45 mg Sertraline 200 mg
3	57y, M	7y	+ IgG	Reduced NAA/Cr vermis 0.79 hemispheres 1.04	Cortical myoclonus	normal	10 Hz	Lithium 408 mg Venlafaxine 225 mg
4	47y, F	10y	–	Reduced NAA/Cr vermis 0.75 hemispheres 0.8	Cortical myoclonus	normal	11 Hz	Lithium 800 mg imipramine 100 mg Olanzapine 25 mg
5	55y, F	30y	+ IgG	Reduced NAA/Cr vermis 0.89 hemispheres 0.85	Cortical myoclonus	normal	10 Hz and first harmonic at 20 Hz	Lithium 675 mg Citalopram 40 mg Quetiapine 100 mg
6	70y, F	20y	+ IgG	ND	Cortical myoclonus	normal	8 Hz	Lithium 400 mg fluoxetine 40 mg
7	42y, F	10y	–	ND	Cortical myoclonus	normal	13 Hz	Lithium 1000 mg Quetiapine 650 mg Sertraline 100 mg
8	66y, M	29y	–	ND	Central tremor	normal	6 Hz and first harmonic at 12 Hz	Lithium 800 mg Flupenthixole 0.5 mg

MRS Magnetic resonance spectroscopy, ND not done, SEP somatosensory evoked potentials
^aThe NAA/Cr, N-acetyl-aspartate/creatine. This was measured in the vermis and cerebellar hemispheres (normal values Vermis > 0.95, hemispheres > 1.00
^bThe P₁N₂ and the P1N3 components were enlarged, above 14 μV (Fig. 1b)
^cJLA, jerk locked averaging and CC, cross correlation analysis were applied in cases 1–8, results are shown in Figs. 1, 2, 3 and 4
^dAll patients had lithium serum levels within the normal range: 0.4-1 mmol/L and all received a dose below 1200 mg/die of lithium carbonate or equivalent dose of lithium citrate (liquid preparation)
^eCases 1 to 7 presented with a quasi-regular tremor while case 8 was rhythmical. Frequencies were estimated with the in-built FFT function in spike 2 software on 20 s epochs of EMG recordings during upper limb maintenance of anti-gravity posture

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