26 - Sciatic Nerve Injury Flashcards
Case 1
A 55-year-old female presents with a 1-week history of difficulty walking and persistent pain in her left foot. She state that when she lifts her left leg to walk it is like her foot is dead, it just” kind of drops”.
What is the history 2 weeks prior to seeing you?
2 weeks prior, she had received an IM injection of 60 mg ketorolac in her left buttock from her PCP for the treatment of foot pain from a non-displaced cuboid fracture in her right foot due to an inversion injury suffered when she fell in a hole and landed on her back.
She was immobilized in a surgical boot and told to bear weight as tolerated, use ice and elevate the right leg.
What happened for the remainder of the first week?
For the remainder of the first week, she continued to experience pain and swelling of her left ankle and foot and difficulty walking. She has persisted in having tenderness along the first and second metatarsals. Her radiographs one week ago were negative for signs of stress fracture of the left forefoot.
She states that although she is able to feel everything, her left leg and foot feel “dead”.
She still might have a stress fracture, but it would not be evident on a radiograph at this point
What happened one week ago?
One week ago, her PCP told her it is likely overuse due to favoring the right foot, prescribed ibuprofen 800 mgs tid, and referred her to you for a second opinion.
What else is in her past medical history?
Other than this incident her medical history is unremarkable other than for occasional asthma for which she uses an albuterol inhaler prn and the ibuprofen as initially prescribed. She is on no other medications.
What are the findings on the physical exams?
- VSS
- Mild swelling over right lateral midfoot with pain upon palpation of the cuboid. Mild swelling on the dorsal and plantar aspect of the left forefoot, but no pain with palpation.
- Anterior and peroneal muscle group rated at 3/5, posterior and medial muscle groups 5/5
What does this muscle weakness mean?
- There is a problem with the common peroneal nerve
- This would lead to the muscle weakness we see as well as the drop foot
What is the general rule of thumb for standing on heels/tip toes?
Patient can stand on tip toes but not heel, peripheral neuropathy caused by metabolic problem
If the patient can stand on their heel, but not on the tip toes, it is caused by a CNS tumor
How does this patient present in terms of heel/toe weakness?
She is unable to stand on her left heel yet is able to stand on her toes.
How is the sharp/dull sensation in this patient?
Sharp/dull sensation is reduced on the dorsum of her left foot-other neurological exams WNL
What is on the differential?
- Trauma to L4-L5
- Masses
- Compartment syndrome
- Diabetic mononeuropathy
- Vasculitis
Describe a trauma to L4-L5
- Direct injury to the sciatic nerve (L4, L5, S1, S2, S3), primarily to the peroneal branch, from the needle, itself; chemical irritation from the solution, itself; hematoma leading to ischemic injury to nerve
- L4, L5 disc injury from fall
What does the acute onset suggest?
Trauma, rather than a mass or vasculitis/neuropathy
What studies would you like to do in this case?
- EMG (electromyography)
- NCV (nerve conduction velocity - can do motor or sensory)
- MRI (sciatic nerve)
Would probably want to do a motor NCV due to the muscle weakness
What are the results of the motor nerve conduction velocity?
Left peroneal nerve
- 16.7 m/sec
Right peroneal nerve
- 72.5 m/s
Fibular head to extensor digitorum brevis is the nerve we measure
What is a normal NCV in the leg?
50-60 m/sec
Describe the NCV test
- Distance between the proximal and distal stimulation points (mm)
- Difference in time between the onset of the CAMP (compound action muscle potential) when the proximal electrode stimulated minus the distal electrode stimulation (msec)
- Distinguishes demyelinating from axonal diseases
What is the CMAP (compound muscle action potential) in this patient?
- The CMAP (compound muscle action potential) demonstrated an increased latency and a slightly decreased amplitude with left peroneal stimulation
- Additionally, spontaneous fibrillation of the tibialis anterior and short head of the biceps femoris on the left were observed.
These are NOT normal findings
What do you see in demyelinating diseasing?
NCV is SLOWER
- the NCV is slowed to 50% normal
- the amplitude is generally normal
- the distal latency is prolonged
What do you see in axonal diseases?
NCV is only SLIGHTLY slower
- the NCV is slowed only slightly
- the amplitude is lowered
- the distal latency is normal
What happens when myelin is gone?
Without myelin, the nerve impulse is slowed, but speed of impulse not altered with axonal damage in teh presence of normal myelin
NCV normal in myopathies and disorders of the anterior horn
What level of activity will be normal in the muscle at rest?
Normally there is no activity of the muscle at rest, but fibrillations suggest acute denervation, acute metabolic neuropathies or polymyositis
What is the diagnosis in this case?
Sciatic nerve injury
90% of patients have immediate symptoms
How do you treat the sciatic nerve injury?
- Inject 3-5 mls of normal saline into the subgluteal space - DILUTE the area
- Consider early PT with strengthening exercises and use of a flexible dropfoot brace - IMMEDIATELY PT
- Consider neuropathy drugs (gabapentin, pregabalin, duloxetine)
