LONG LATENCY REFLEX (LLR)
Introduction
Long latency reflexes are absent in healthy subjects when muscles are at rest. Its presence in patients at rest suggests a hyper-excitability of the central part of the reflex loop, i.e. the sensorimotor cortex. Abnormal LLR usually occurs with a latency of about 40 msec, also called as the C-reflex. LLRs are present in contracted muscle but not in relaxed muscles in healthy individuals. However abnormal LLR are usually well synchronized and have biphasic morphology. C-reflex in a myoclonic patient means that myoclonus is reflex in nature or sensitive to somatosensory stimuli. Hence C reflex is similar to a reflex myoclonus since both are motor responses to sensory stimuli. In a patient with myoclonus, the existence of a C reflex in muscles even without giant SSEPs can be considered as cortical reflex myoclonus. This can be confirmed by EEG back averaging or coherence analysis techniques. The physiological correlate of reflex myoclonus is the C-reflex. In organic myoclonus syndromes, due to the hyper-excitable cortex, the C-reflex has very short latencies with a range of 40-50 ms (upper limb). In psychogenic reflex myoclonus, the latencies are longer than 100 ms
Method
LLRs can be recorded with surface electrodes by stimulating median nerve. The median nerve is stimulated at the wrist at 2–3 Hz just above motor threshold. EMG responses are recorded from wrist extensors, APB or first dorsal interossei muscles and averaged (100 sweeps). The EMG signals could be rectified to prevent phase cancellation but this is not necessary for LLR as they are usually synchronized like M or H waves which are also displayed even without rectification.
Responses
1. M reflex
2. H reflex 30 msec
3. LLR1 40 msec (upper limb), not seen normally even with sustained muscle contraction (Only 10% of normal have it on sustained muscle contraction). So its presence even on sustained contraction can be abnormal and so also at rest. LLR1 is mostly enlarged or present in cortical myoclonus
5. LLR2 50 msec, seen normally with sustained contraction
Both LLR should be absent in rested state
Enlarged in cortical myoclonus and reflex reticular myoclonus
6. LLR3 at 70 msec can sometimes be seen.
SOMATOSENSORY EVOKED POTENTIAL
Method
Stimulation threshold 10-15% above the motor threshold (Like in LLR)
Montage (Median SSEP)
CP4-A2
CP3-A1
CP4-Fz
Cp3-Fz
CP3/4-A1/2 may have far field potential
Interpretation (Median SSEP)
N20/P25 enlarged >7.5-10 microvolts
Or enlarged N35 (P25-N35 amplitude) >7.5-10 microvolts
Major components of Median nerve SSEP are the N20, P25, N33 and N60 potentials
Unverricht Lundborg
Progressive myoclonic epilepsy (EPM1), which is also known as syndrome has enlarged N20, P25 component of SSEP.
Lafora body disease
Enlarged N20, P25 component along with enlarged N60 wave, which is not seen in EPM1.
Tibial SSEP interpretation
P37 and following negative amplitude: Enlarged when amplitude >15 microvolts
SPS (STIFF PERSON SYNDROME)
Spread of reflex
(1) Sural stimulation and record from Paraspinal, Quadriceps, Gastrocnemius, Tibialis Anterior (TA), and Hamstrings muscles. Normally only TA and Hamstrings show activity. In SPS, Paraspinal, Quadriceps and Gastrocnemius muscles also may show activity, which is not normally present.
(2) Stimulate Posterior tibial and record from Quadriceps and Paraspinal muscles. Single stimulation and trains of stimulation. Normally nor activity should be seen.
(3) Stimulate median nerve and record from deltoid, SCM and paraspinal muscles.
Single stimulation and trains of stimulation. Normally nor activity should be seen.
(4) In patients with SPS, unexpected noises often trigger violent muscle jerks resulting in falls
Reflex spasmodic myoclonus/ stimulus induced truncal myoclonus
A unique motor response, stimulus-induced truncal myoclonus, is seen in SPS. Median nerve stimulation produces one to three synchronous myoclonic bursts, lasting 60 to 70 milliseconds, followed by a tonic decrescendo activity. The recruitment order of muscles suggests that this is generated in spinal cord and travels via propriospinal tracts.
Continuous EMG activity of needle EMG
When muscle is relaxed or when antagonist muscle is contracted.
Exaggerated startle
sound, touch, cutaneous stimulation or blink reflex produced generalized spasms that may last for many minutes
TCR (Trigeminal Cephalic Reflex)
TCR: Supine position,
Glabella tap
Trapezius contraction (SLR 17-25 msec, LLR 50 msec)
H/M ratio
Ration of Maximum H amplitude to maximum M amplitude. This ratio is increased, commonly above > 0.7.
HYPERPLEXIA (FAMILIAL AND ACQUIRED)
Method:
1. Supraorbital nerve stimulation, 0.2 msec, 3x sensory stimulation
2. Glabellar tap
Active electrode : Trapezius
Trapezius contraction (SLR 17-25 msec, LLR 50 msec)
Multi-channel sEMG recording
The first response is from both bilateral orbicularis oculi (onset latency 9–20 ms with taps on the nose or jaw, ≤ 30 ms with auditory stimuli). Orbicularis oculi response is not a part of the startle reflex (SR) as it does not habituate, unlike other responses. The first EMG response of the SR is in from SCM muscle, followed by the masseter, trunk, and limb muscles.
Duration
Duration of EMG burst is between 150 and 400 ms. Reticular myoclonus has much shorter burst duration, closer to cortical myoclonus duration.
Latencies
Startle reflex shows much longer latencies from cranial muscles to intrinsic hand and foot muscles compared to the Reticular myoclonus.
Habituation
In normal subjects, SR habituates after a few attempts, unlike in Hyperekplexia.
MYOCLONUS
FUNCTIONAL MYOCLONUS
Salient points
(1) Jerks with bursts of EMG of long duration (usually > 70 msec)
(2) Well organized triphasic pattern of activation of agonist and antagonist muscles.
(3) Stimulus-evoked jerks or jumps with variable latencies (usually > 100 msec) and variable muscle recruitment. In psychogenic reflex myoclonus, the latencies are longer than 100 ms. Abnormal C-reflex has very short latencies with a range of 40-50 ms
(4) Apparent startle response may not be preceded by contraction of orbicularis oculi or a cranio-caudal progression of activation of muscles.
(5) A Bereitschaftspotential (pre-movement potential) may precede psychogenic jerks
Functional propriospinal myoclonus
(1) Absence of a typical rostral and caudal recruitment order
(2) Burst duration longer than 1,000 ms
(3) Isolated muscle activity in the rectus abdominis muscle
PROPIOSPINAL MYCOLONUS
(1) Flexion arrhythmic jerks in the truncal axial muscles, hips and knees.
(2) It may or may not be stimulus sensitive and often becomes more frequent when the individual is lying in a supine position.
CORTICAL MYOCLONUS
Enlarged SSEP [LINK]
Abnormal Long Latency Reflex [LINK]
CERVICAL DYSTONIA
1. TCR (TRIGEMINOCEPHALIC REFLEX): inhibitory
Oligosynaptic externoceptic suppressive reflex.
Method:
Maintain sustained bilateral SCM contraction (elevate the head by 30 degree)
Active surface EMG electrode on SCM
Passive surface EMG electrodes on Clavicle
Supraorbital nerve stimulation, 0.2 msec, 3x sensory stimulation
multiple averages: P19/ N31 waveform amplitude <10 microvolts in cervical dystonia
2. Blink reflex recovery
Record two blink responses at 100 and 200 msec ISI
R2 conditioned/ R2 unconditioned area >30% is abnormal suggesting
BLEPHAROSPASM
Blink reflex method
Superior orbital nerve stimulation (15-25 ma)
Increase stimulation till maximum R1 amplitude.
recording form orbicularis oculi
Blink reflex recovery
Record two blink responses at 100 and 200 msec ISI
R2 conditioned/ R2 unconditioned area >30% is abnormal.
Interpretation
Suppression of R2 is less in cranio-cervical and generalized dystonia but normal in focal dystonic of arm like writer's cramp. Comparison can be made between amplitude of R2 and R2’ or product of R amplitude with R duration and product of R’ amplitude with R’ duration. A more accurate way is to compare R2 and R2’ areas.
Calculation of R2 area for Blink reflex recovery: The area of R2 and R2c responses can be obtained by multiplying the peak-to-peak amplitude by the duration of the response.
PROGRESSIVE SUPRANUCLEAR PALSY
TCR (TRIGEMINOCEPHALIC REFLEX)
Method
Active electrode: C3 paraspinal position (semispinalis capitis muscle)
Passive electrode: C7 spinous process
Supraorbital nerve stimulation, 0.2 msec, 3x sensory stimulation
Interpretation
10 trials: 80% persistence normal
amplitude >30 microvolt above baseline is normal
Absent in PSP, present in MSA and PD
Blink reflex with Median nerve stimulation
Patients with PSP had no response from orbicularis oculi muscle but a positive response in mentalis muscle on stimulating the median nerve.
TREMOR
FUNCTIONAL TREMOR
Entrainment
Tapping at 1hz, 3hz and 5hz with one hand and tremor recording from the other hand.
The tremor gets entrained at tapping frequency.
High coherence between the tapping signal and tremor signal. Use EMG for coherence analysis as accelerometer may give false positive result.
Pathological shift
Tapping at 1hz >20% frequency change
Tapping at 3hz > 25% frequency change
Tapping at 5hz > 25% frequency change
Ballistic movement
Amplitude of tremor reduced by 50%
Tremor pauses
Trials >5/10 need to be positive
Loading (250gm weight)
Amplitude increase by 30%
General analysis
1. Frequency
2. Amplitude
3. Harmonics
4. Waveform symmetry
ENHANCED PHYSIOLOGICAL TREMOR VS ESSENTIAL TREMOR
Load wrist with 500gm weight
Enhanced physiological tremor frequency reduces
Essential tremor frequency remains same
PARKINSON'S DISEASE TREMOR VS ESSENTIAL TREMOR
Tremor wave form in PD tremor is asymmetrical
Multiple harmonics on power spectrum
ORTHOSTATIC TREMOR
Highest frequency tremor 13-17hz
Multiple harmonics on power spectrum (EMG)
High inter-limb coherence (EMG)
RUBRAL TREMOR
Low-frequency tremor 2-4hz
Present at rest, posture and action