Spinal Epidural Lipomatosis

Spinal epidural lipomatosis is abnormal overgrowth of unencapsulated epidural fat that compresses the thecal sac and nerve roots, most often in the thoracic or lumbar spine. It is caused by exogenous corticosteroids (long term or high dose), obesity (body mass index over 30 kg/m2), Cushing syndrome, hypothyroidism and, rarely, idiopathic. Males are affected more than females. Prevalence is about 2 to 3% in some series.

Pathophysiology. Excess fat deposition in the epidural space narrows the canal, causing compressive myelopathy, radiculopathy or neurogenic claudication.

Back pain, radicular leg pain, neurogenic claudication (pain on walking relieved by flexion), leg weakness, sensory loss, and, in severe cases, cauda equina syndrome (retention, incontinence, saddle anaesthesia) or thoracic myelopathy (spasticity, gait disturbance). Symptoms develop over months in most.

Red flags.

• Acute bladder or bowel dysfunction, saddle anaesthesia or rapidly progressive weakness.
• Severe myelopathic signs.

MRI of the spine is the test of choice: abundant epidural fat of high T1 and T2 signal with narrowing of the thecal sac ("Y-sign" or stellate sign in the lumbar region), with grading by the degree of canal compromise. CT or CT myelography if MRI is not possible. Check cortisol (exclude Cushing syndrome), thyroid function, glucose, and review steroid use and weight.

Differential diagnosis.

• Degenerative lumbar stenosis, disc herniation and epidural abscess.
• Epidural haematoma, metastasis and lymphoma.
• Peripheral vascular claudication.

Remove the cause. Reduce or stop exogenous corticosteroids when possible (taper to avoid adrenal insufficiency), treat Cushing syndrome and hypothyroidism.

Weight loss. Diet, exercise and, where eligible, bariatric surgery or glucagon like peptide-1 receptor agonists. Weight loss of 10 to 15% or more can reduce symptoms and fat volume.

Symptom control. Analgesia (paracetamol, short courses of anti-inflammatory drugs where safe), neuropathic agents (gabapentin 300 mg daily, increased to 600 to 1200 mg three times daily, adjusted to eGFR), physiotherapy and epidural injections used with caution (steroid injections can worsen the lipomatosis).

Surgery. Decompressive laminectomy with removal of epidural fat for progressive deficit, severe myelopathy, cauda equina syndrome or failed conservative treatment. Outcomes are good for pain, and less so for established motor deficits.

Monitoring. Neurological examination, weight, steroid dose and MRI if symptoms change.

Referral and escalation. Refer urgently to spinal surgery for neurological deficit.