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Case Study by Neurosurgeon Dr Damian Amato

Thursday 23 October 2014

Case Study by Dr Damian Amato

The case presented here has two very interesting features; the diagnostic challenge and the histopathology with its associated prognosis.  

Presentation: A 69 year old lady presented with three weeks of increasing left leg weakness.

The weakness included both proximal musculature (hip abductors and quadriceps) as well as lower leg muscles (plantar and dorsiflexors of the ankle/toes). The weakness was not associated with any numbness or any significant pain.

Background: The patient was referred from Orthopaedic surgeon Dr Peter Johnstone who had previously treated her knee osteoarthritis and also her spinal stenosis four and a half years earlier.

She had bilateral knee replacements and a decompression laminectomy from L3-L5. There was no history of malignancy and no other significant medical history to note.

Examination and Investigations: The examination was as per the orthopaedic referral with weakness in the left lower limb (3-4/5 in the muscle groups described), no significant weakness not the right.

No sensory changes were identified, reflexes were difficult to elicit bilaterally partly due to previous knee replacements. The MRI of the lumbar spine demonstrated the previous laminectomy with evidence of post laminectomy anterolisthesis at L3/4 producing foraminal stenosis and therefore bilateral L3 nerve root compression which was worse on the left.

Additionally, there was also a foraminal/far lateral disc protrusion at L5/S1 on the left producing left L5 nerve root compression.

Discussion: The above findings can only partially explain the left leg weakness. L3 compression can cause quadriceps weakness and L5 ankle dorsiflexion weakness. However there was more global weakness. Could the anterolisthesis be producing a cauda equina syndrome?

The anterolisthesis or forward slip produced foraminal stenosis and bilateral L3 nerve root compression but not enough in the way of central stenosis to explain the symptoms. Additionally the symptoms were solely weakness without pain and were unilateral. Further investigation was warranted.

Dynamic X-rays of the lumbar spine and an MRI of the brain and cervical and thoracic spine were performed. The X-rays showed no increase in the anterolisthesis on forward flexion, excluding a dynamic instability.

The MRI brain demonstrated a rounded 12mm lesion in the right percent real gyrus. There was minor peripheral enhancement of the lesion with gadolinium and surrounding FLAIR hyperintensity.

Management:  Differential diagnose included cerebral access, metastatic tumour, atypical demyelination, or high grade glioma. A stereotactic craniotomy and biopsy was performed to identify the lesion. A further MRI was performed for intra-operative navigation using the Stealth system and biopsies taken. Post-operative improvement in left leg power was noted once dexamethasone was commenced. Histopathology revealed features consistent with an active inflammatory demyelination process (tumefactive MS/demylelinating pseudotumour).

Once the final diagnosis was established a neurology opinion was sought from Dr Chris Staples. Treatment consisted of Methotrexate and Prednisolone.

Ongoing improvement has occurred with progression of mobility from a wheelie walker to Canadian crutches. A follow-up in 12 months’ time with a repeat MRI has been arranged.

Summary: The case outlined was interesting from a diagnostic point of view. Commonly in neurosurgery the diagnostic heavy lifting has been done by the GP or other specialists with the patient presenting with their diagnosis from the outset.

This case also highlights the differential diagnoses of cerebral mass lesions. Too often these lesions are those confer poor prognosis with dismal outcomes in the setting of malignancy.

The involvement of many team members was central to this patients' care. Her GP, orthopaedic surgeon, radiologists, treating neurosurgeon and neurologist and pathologists, nursing staff in theatre and the ward as well as physiotherapists.