Mirror Movements (Spiegelschrift)
1st described by Dr. Friedrich Albrecht Erlenmeyer (1849–1926)
Grundzüge ihrer Physiologie und Pathologie, 1879
Definition
"Involuntary movements on one side that mirror voluntary actions on the other"
-Normal in <7–10yo (CC myelination), 70% healthy children (on speed-based task)
Pathophysiology
Three teories
-Overflow
> signal 'overflows' to the other hand
-Weak interhemispheric inhibition
> both hemispheres fire together
-Abnormal crossing motor pathways
>same commands go to both hands
Key quests
-Development & family history
-Cognitive & neuropsych
Exam
-Rapidly finger‑tap, open/close the fist, or perform pronation-supination
>MC in UEs
>Watch the “quiet” hand
-Woods & Teuber scale
0→ none
1→ barely
2→ clear, mod amplitude (<50%); 2a (slight) & 2b (strong)
3→ clear, large amplitude (>50%)
4→ complete, unable to supress
W&T=0
No clear imitative movements. Right hand is active and left hand is scored
W&T=1Barely discernible repetitive movements. Right hand is active and left hand is scored
W&T=2a
Slight mirror movements. Right hand is active and left hand is scored
W&T=2b
Stronger, but briefer, repetitive movements. Right hand is active and left hand is scored
W&T=3
Strong and sustained repetitive movements. Left hand is active and right hand is scored
W&T=4
Movements equal to those observed in the active hand. Left hand is active and right hand is scored
Diagnostic work-up
-Affect QoL, otherwise no need
>Children unable to climb a ladder because releasing one hand makes the other involuntarily release too
>Painful compensatory shoulder contractions while writing
-Adults→ secondary (affecting CST)
>normal: fatigue, stress, high cognitive load, and aging
>investigate, if new in adulthood
Electrophysiology
-TMS
>Patho: simultaneous response & normal latency
>Physio: delayed responses & longer latency
-EMG: synchronous recruitment of homologous muscle groups, often with near‑identical timing to the voluntary contraction
-CMM demonstrates coactivation without delay
Neuroimaging
-bMRI to evalaute CC
>DTI→ ↓FA CC
>Asymmetric sigmoid bundle
-fMRI→ resting‑state
-c-spine MRI
>spine abnormality
>vertebral fusion→ KFS
Genetic
-DCC (>80% of cases), followed by RAD51, NTN1, and ARHGEF7
Clinical Pearls
MM vs synkinesias
-Synkinesia→ no mirror
MM vs Imitation
-Imitation→ frontal lobe disinhibition (≠ behavior)
MM vs affected hand
-PD→ less affected hand
-CBS/CJD→ more affected hand
*MM co-exist w/ alien hand phenomenon: early (CJD) vs late (CBS)
-ET→ either
-HD→ UHDRS TMS correlated w/ MM
Treatment
-PT/OT→ bimanual independence, adpt at school/work
>HABIT-ILE→ CP-related MM
-Botox→ contralateral dystonia
-PD→ dopamine therapy adjustment
-Surgical→ no effect
-TMS→ research
Etiology
CMM
Mutations affecting CST
-DCC: req for CST axon guidance
-NTN1: chemoattractant for decussating CST axons
-RAD51: axonal migration & midline crossing indirectly
-ARHGEF7: cytoskeletal remodeling for CST
DCC
DCC
RAD51
PD
May precede motor asymmetry
-Asymmetric DA degeneration
-Loss of striato‑thalamo‑cortical regulation of motor suppression
-Inc motor overflow 2/2 impair inhibition
PD
PD
PD
-not really MM, but overflow
-RSM w/ mouth moves
LIDOthers
-Focal hand dystonia
>if contralateral use, MM-dystonia
>Botox contralateral
>Rare sensory coupling
-Klippel-Feil syndrome
#FND→ TMS
-Other craniovertebral anomalies
#KFS
-Kallmann syndrome
-Joubert syndrome
-Stroke
>R MCA territory infarct
>Limitation QoL
-CJD
-Tumor
>M1 resection
-KMT2B
Others
-ALS
-HD