EMG lower extremities

[Dansk2011]

Starting doing EMGs again for the hospital because of need. Don't mind doing them although the learning curve has been a bit challenging. I seem to have issues getting accurate lower extremity sensory studies if I can even get them at all despite repositioning electrodes and shocking what seems to be like a 100 times. Often times the abnormalities don't seem to be clinically relevant or add up to what they are experiencing. Any suggestions or advice? Don't have a great way of warming outside of heating pads unfortunately. Most of them are older patients so that likely contributes. Hate doing lower extremities in general and this certainly doesn't help.

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[runfastnow]

IMO from a sports/spine physiatrist at an ortho practice primarily looking for radic - low yield for killing yourself (or patient) over lower extremity sensory studies unless high concern for some sort of polyneuropathy or specifically asked to rule that out. Sural is hard to find and can be impossible with anyone with a high BMI. I just comment sural/sensory abnormalities (such as non-response) are likely technical in nature due to BMI, age, etc. and clinically irrelevant to the radic, etc.

Unless I REALLY need the sural or sensory information I shock it 10-15 times and if I can't get it then move on to motor studies and EMG.

 

[JBM16BYU]

A good rule of thumb for some of the lesser-used lower limb sensory studies (superficial fibular sensory, saphenous sensory, even medial plantar) is to evaluate the good / non-affected side first. If present there, then go to the affected side for comparison. If not present on the "normal" side, then no reason to search for it on the abnormal side.

BMI, peripheral edema, age are all reasons that sural sensory can be tricky to find. Most important if you are evaluating for polyneuropathy or a lumbosacral plexopathy. Not super important for a lumbosacral radiculopathy (since those are preganglionic and sensory should be normal anyways).

When you say doing for the hospital, are you talking about inpatient EMGs for the ICU or admitted patients, or are you talking about the hospital is feeding patients to your outpatient clinic?

 

[Dansk2011]

A good rule of thumb for some of the lesser-used lower limb sensory studies (superficial fibular sensory, saphenous sensory, even medial plantar) is to evaluate the good / non-affected side first. If present there, then go to the affected side for comparison. If not present on the "normal" side, then no reason to search for it on the abnormal side.

BMI, peripheral edema, age are all reasons that sural sensory can be tricky to find. Most important if you are evaluating for polyneuropathy or a lumbosacral plexopathy. Not super important for a lumbosacral radiculopathy (since those are preganglionic and sensory should be normal anyways).

When you say doing for the hospital, are you talking about inpatient EMGs for the ICU or admitted patients, or are you talking about the hospital is feeding patients to your outpatient clinic?

That's a good approach. It's all outpatient. I work with the ortho/neurosurgeons. But I get a fair bit of non radicular stuff. A lot of which is fairly obscure evals. Evaluation of superficial peroneal neuropathy, tarsal tunnel/foot numbness, etc. I've actually been getting a lot of post trauma stuff too which has been tough. My hope was that it would be mostly peripheral nerve stuff and radic screens but I've been getting some really funky cases. Diagnosed an isolated spinal accessory injury just a few days ago. A lot do the "radic" screens I've gotten for lowers are older patients (75+) with severe multilevel central and neuroforaminal stenosis without particularly clear cut radicular symptoms ie diffuse symptoms. Trying to not waste time and be efficient but can be tough.

 

[sdnuser001]

Sorry to hijack thread but can anyone with more EMG experience explain what can cause an isolated low proximal median CMAP but with normal sensory? Assuming no evidence on needle EMG for radic

 

[JBM16BYU]

Sorry to hijack thread but can anyone with more EMG experience explain what can cause an isolated low proximal median CMAP but with normal sensory? Assuming no evidence on needle EMG for radic

Essentially a normal median sensory response and low median motor amplitude? I would definitely need more information like presenting symptoms, time course of symptoms, etc.

Just with the information provided, there are a host of things:
-Median neuropathy with a conduction block - SNAP normal. Distal median CMAP normal; low proximal median CMAP (typically >50% drop in amplitude). Needle EMG would show reduced recruitment, but the MUP should be normal.
-Marinacci anastomosis (reverse Martin-Gruber) - SNAP normal. Distal median CMAP would be normal; low proximal median CMAP. This is rare, but occurs from an ulnar-to-median nerve anastomosis, so the distal CMAP would be much higher than proximal CMAP.
-Median neuropathy with isolated motor fascicular involvement - SNAP normal. CMAP low amplitude. If entrapped, typically has demyelinating features (such as prolonged distal latency or slowed conduction velocity).
-C8-T1 radiculopathy - SNAP would be normal since radiculopathies are preganglionic injuries. If the CMAP amplitude is low, you should see abnormalities with needle EMG
-Motor neuron disease - SNAP are normal as it is a disorder of only the lower motor neurons and their axons. CMAP amplitude is low. You should see abnormalities (fibrillation potentials, fasciculations, reduced recruitment, large MUP) on needle EMG.
-Myopathies - SNAP are normal; CMAP amplitude may be low. Many myopathies are proximal; however, there are distal myopathies that recording from the APB muscle on the hand can show low amplitude CMAP. Needle EMG should show early recruitment of small MUP (+/- fibrillation potentials if inflammatory)
-Neuromuscular junction disorders (particularly Lambert-Eaton myasthenic syndrome) - SNAP are normal. CMAP amplitude may be low. Repetitive nerve stimulation after 10-second exercise should show increase in CMAP amplitude by like 200%. Needle EMG shows variable unstable MUP.
-AMAN (acute motor axonal neuropathy, a variant of Guillain-Barre Syndrome) - SNAP are normal. CMAP amplitudes are low. Acute-onset. Needle EMG should show abnormalities.

 

[sdnuser001]

Essentially a normal median sensory response and low median motor amplitude? I would definitely need more information like presenting symptoms, time course of symptoms, etc.

Just with the information provided, there are a host of things:
-Median neuropathy with a conduction block - SNAP normal. Distal median CMAP normal; low proximal median CMAP (typically >50% drop in amplitude). Needle EMG would show reduced recruitment, but the MUP should be normal.
-Marinacci anastomosis (reverse Martin-Gruber) - SNAP normal. Distal median CMAP would be normal; low proximal median CMAP. This is rare, but occurs from an ulnar-to-median nerve anastomosis, so the distal CMAP would be much higher than proximal CMAP.
-Median neuropathy with isolated motor fascicular involvement - SNAP normal. CMAP low amplitude. If entrapped, typically has demyelinating features (such as prolonged distal latency or slowed conduction velocity).
-C8-T1 radiculopathy - SNAP would be normal since radiculopathies are preganglionic injuries. If the CMAP amplitude is low, you should see abnormalities with needle EMG
-Motor neuron disease - SNAP are normal as it is a disorder of only the lower motor neurons and their axons. CMAP amplitude is low. You should see abnormalities (fibrillation potentials, fasciculations, reduced recruitment, large MUP) on needle EMG.
-Myopathies - SNAP are normal; CMAP amplitude may be low. Many myopathies are proximal; however, there are distal myopathies that recording from the APB muscle on the hand can show low amplitude CMAP. Needle EMG should show early recruitment of small MUP (+/- fibrillation potentials if inflammatory)
-Neuromuscular junction disorders (particularly Lambert-Eaton myasthenic syndrome) - SNAP are normal. CMAP amplitude may be low. Repetitive nerve stimulation after 10-second exercise should show increase in CMAP amplitude by like 200%. Needle EMG shows variable unstable MUP.
-AMAN (acute motor axonal neuropathy, a variant of Guillain-Barre Syndrome) - SNAP are normal. CMAP amplitudes are low. Acute-onset. Needle EMG should show abnormalities.

Got it thanks! And my mistake I meant that the only abnormality was that the DISTAL CMAP was low. But sensory studies and motor latencies normal. I can't remember the exact situation but believe it was a CTS screen in a younger patient. Could this be some kind of anastomosis?

 

[JBM16BYU]

Yes, the most likely things for a low distal median CMAP amplitude with completely normal needle EMg are:
1. Incorrect placement of the APB G1 electrode
2. Under stimulation
3. Anastomosis. If the distal median CMAP is low compared to the proximal at the elbow, you likely have a Martin-Gruber. Keep the G1 electrode on APB and instead stimulate from the ulnar wrist and ulnar below the elbow to see if that accounts for the loss in median amplitude. You may find when performing the ulnar studies that your distal ulnar CMAP amplitude looks high in comparison to the below the elbow amplitude, indicating that a portion of the median nerve has anastomosed in the forearm to the ulnar nerve.

 

[sdnuser001]

Yes, the most likely things for a low distal median CMAP amplitude with completely normal needle EMg are:
1. Incorrect placement of the APB G1 electrode
2. Under stimulation
3. Anastomosis. If the distal median CMAP is low compared to the proximal at the elbow, you likely have a Martin-Gruber. Keep the G1 electrode on APB and instead stimulate from the ulnar wrist and ulnar below the elbow to see if that accounts for the loss in median amplitude. You may find when performing the ulnar studies that your distal ulnar CMAP amplitude looks high in comparison to the below the elbow amplitude, indicating that a portion of the median nerve has anastomosed in the forearm to the ulnar nerve.

Awesome thanks so much!