IS IT RADICULOPATHY OR A NERVE INJURY? CAN THIS DIFFERENTIATION BE SO EASY?

Many times a very simple looking case can also turn out to be complicated. We as electrophysiologist need to be thorough with anatomy, clinical reasoning, understanding of the conditions under scanner and it is only then we can make an accurate confirmation.
There may be two views regarding this.

1. We are performing electrophysiological studies. We should be concerned only with electrophysiological conclusion. It is a consultant's job to come to a conclusion.Why should we break our head
2. Let us see the patient as a whole.Let us correlate electrophysiological findings with clinical features of the patient.This will help the consultant to make better and faster decision.This will also help the patient.

If we sit on a patient's side, as a patient what will we expect after spending so much for a test? Sitting on a consultant side, what will we expect from a test? We need to work taking this view point and then decide. I wouldn't force anyone to adopt any approach which doesnt digest to their minds

Few days back, there was a patient which I would like to share. Patient came with the reference EMG NCV studies with no provisional diagnosis.

INTRODUCTION OF THE CASE

77 years old patient who was operated twice in the spine. Initially he was operated for L-4-5 Discectomy. Few months later when again he started having symptoms, he was operated again. This time it was Laminectomy with screw fixation for the same level. After this second surgery things were going on well and he had a normal neurology for two days. Suddenly after two days patient developed foot drop on the left side. He was taken inside the operation theatre again to realign the pedicle screw, but this did not cure his foot drop. When patient came for EMG/NCV studies, it was 4 months post his second surgery and he still had foot drop

There can be two differential diagnosis in this case

1. Spinal nerve root compression at L-4-5-S1 level. This can either be a new lesion developed due to improper screw placement that affected the same segment or the oedema post surgery in the operated area compressed the nerve root giving rise to a new acute injury
2. Post operatively patient persistently lied down with externally rotated foot which injured Peroneal nerve around Fibular head

Patient was tested with NCV and EMG studies. Let us understand each aspect of the test performed with a logical reasoning

The above table is for Motor Nerve conduction study. If we analyze the table, MNCV both Tibial nerves within normal limits with normal distal motor latencies and CMAP amplitudes. CMAP amplitudes look bilaterally comparable. Hence this showed there was no problem with the (lt) Tibial nerve

MNCV (rt) Peroneal nerve in the leg and across the knee was normal with normal distal motor latency and CMAP amplitude. 

On the (lt) side, Peroneal nerve MNCV and distal motor latency was within normal limits, but there was a marked reduction in CMAP amplitude.

Usually NCV studies are normal in radiculopathy as the lesion lie proximal to the formation of the nerve unless the nerve root injury is severe enough to cause axonal loss of the affected spinal nerve root.

Analyzing the MNCV of Peroneal nerve, we could trace one problem and that was reduced CMAP amplitude in (lt) Peroneal nerve which suggest axonal loss in the Peroneal nerve.
Peroneal nerve MNCV is performed with recording electrodes at Extensor Digitorum brevis muscle. EDB has predominantly L5 myotome. 

So once again this does not clear whether it is a spinal nerve root injury or Peroneal nerve injury

Above table is the table of Sensory nerve conduction study performed with orthodromic technique. Sural nerve showed normal configuration in terms of latency and amplitude. But Superficial Peroneal nerve showed reduced amplitude which again predict axonal loss.

EMG study using concentric needle electrode was performed. In order to rule out Radiculopathy versus Peroneal nerve injury, we need to perform EMG accordingly.

Peroneal nerve at the fibular head divides into Superficial and Deep Peroneal nerves

Hence to rule out Peroneal nerve injury, we need to perform EMG study for muscles supplied by Superficial and Deep Peroneal nerves

Additionally if we have to do the study for Radiculopathy, we need to find the exact spinal nerve root affected. So we need to screen from L4 to S2 myotome and by protocol we perform EMG such that we test muscles of two different nerve muscles with same nerve root. This rules out Peripheral nerve injury.

Here Quadriceps femoris (L3-4, Femoral nerve), Tibialis Anterior (L4-5, Deep Peroneal nerve), Peroneus Longus (L5-S1, Superficial Peroneal nerve), Tibialis Posterior (L5-S1, Tibial nerve), Soleus (S1-2, Tibial nerve). 

Quadriceps and Soleus showed normal configuration motor unit action potentials with good and normal recruitment. 

Presence of Fibrillation Potentials in Tibialis Anterior, Peroneus Longus and Tibialis Posterior suggested signs of acute denervation.

Analyzing according to the myotomes, 

 Fibrillation Potentials present in Tibialis Anterior and absent in Quadriceps ruled out any problem with L4 spinal root. Yet since they were present in Tibialis Anterior, L5 root or Peroneal nerve seems involved. Presence of Fibrillation Potentials in Tibialis Posterior ruled out Peroneal nerve injury because Tibialis Posterior is supplied by Tibial nerve.

Hence our diagnosis now got shifted to radiculopathy. And looking to the picture all muscles supplied by L5-S1 had Fibrillation Potentials. We confirmed L5 as affected root because we tested L5 root of various nerves. Now Soleus showed normal configuration activity which ruled out S1-2 roots.

Hence analyzing the entire above picture, we could conclude that this patient had axonal degeneration of L5 spinal nerve root

Analyzing severity of the axonal loss and regeneration

There was no Voluntary activity present in Tibialis Anterior. Hence distally EDB was not tested. And whatever the axonal loss was severe. Even Peroneus Longus and Tibialis Posterior showed poor recruitment and few MUAP which again confirmed severe axonal loss. 

Ideally we should have done EMG for Lower lumber Paraspinals which can increase the specificity of the study. But since the patient was operated twice at that level, there could be signs of acute denervation there also as the incision could have cut the small nerves.This could have given a false positive and biased result. Hence Lumber Paraspinals were not checked with needle EMG

 Hence the final conclusion was

This study was performed considering patient as a whole. Satisfaction seen in the eyes of the patient does boost our motivation to keep doing ideal and ethical work which can benefit the patient

Your valuable feedback on this study will help me enhance my diagnostic skills.