Idiopathic Lumbar Epidural Lipomatosis

We present two cases of idiopathic spinal epidural lipomatosis. Case 1: A 77-year-old man experienced tightness in bilateral lower extremities and neurogenic claudication for 1 year. He was overweight with a body mass index of 30.8 kg/m2. Magnetic resonance imaging revealed extensive epidural lipomatosis of lumobsacral spine with significant constrictive compression of the thecal sac. Case 2: A 78-year-old man presented with low back pain along with progressive pain and numbness in the left lower extremity and neurogenic claudication for 6 months. He was diabetic with body mass index of 25.6 kg/m2. Magnetic resonance imaging demonstrated circumferential compression of the thecal sac due to increased epidural fat tissue at the L4 level. We suggest that spinal epidural lipomatosis should be considered in the differential diagnoses when patients with neurological symptoms have conditions relating to hyperinsulinism such as obesity and exogenous steroid administration.


Introduction
Spinal epidural lipomatosis (SEL) is a rare condition characterized by abnormal accumulation of unencapsulated epidural fat. Most patients with SEL are associated with the administration of exogenous steroids or several endocrinopathies including Cushing syndrome and hypothyroidism [1][2][3][4][5][6][7][8][9]. Idiopathic SEL, defined as cases without evidence of definite predisposing factors, seems to occur in obese patients but pathophysiology remains unclear [10][11][12]. We report two cases of idiopathic SEL with a review of literature.

Case 1
A 77-year-old man experienced tightness in bilateral lower extremities and neurogenic claudication for 1 year. Over past few months, his gait disorder gradually worsened. He had no history of steroid use or endocrinopathy. On examination, he was overweight with a body mass index (BMI) of 30.8 kg/m2. He had no evidence of motor or sensory deficits. Magnetic resonance imaging (MRI) revealed extensive epidural lipomatosis of lumobsacral spine with significant constrictive compression of the thecal sac ( Figure 1). An L4-L5 decompressive laminectomy with removal of the epidural adipose tissue was performed. The histopathological examination confirmed normal adipose tissue. The patient recovered completely.

Case 2
A 78-year-old man presented with low back pain along with progressive pain and numbness in the left lower extremity and neurogenic claudication for 6 months. He had diabetes but had no history of steroid administration or endocrinopathy. His BMI was 25.6 kg/m2. Neurological examination showed no muscle weakness and no sensory deficit. MRI demonstrated circumferential compression of the thecal sac due to increased epidural fat tissue at the L4 level ( Figure 2). Histologic analysis revealed unencapsulated adipose tissue. An L4 laminectomy and removal of excessive adipose tissue was performed. After surgery, the patient's symptoms resolved.

Discussion
Exogenous steroid administration and endocrinopathies such as Cushing syndrome and hypothyroidism are known predisposing factors for SEL [1][2][3][4][5][6][7][8][9][10][11][12]. Widespread use of exogenous steroid, increase in the prevalence of obesity with improving diagnostic modalities should have been the reasons for growing reports on SEL. Although the pathological mechanism of SEL still remains unknown, insulin seems to play an important role. The association of obesity and diabetes in our patients suggests a metabolic syndrome associated with insulin resistance, leading to hyperinsulinism. Steroid also accelerates secretion of insulin, leading to inhibition of lipolysis. It is proposed that hyperinsulinism caused by metabolic syndrome or steroid intake inhibits mobilization of fatty acids (lipolysis) of the central adipose tissue at the site of abdominal or spinal epidural space. The symptoms depend on the level of canal compromise, with thoracic levels causing myelopathy and at lumbar levels resulting in radiculopathy or cauda equina syndrome. In general, the onset of symptoms is gradual and the condition progresses slowly. Some reported cases with acute onset or rapid progression of symptoms might be associated with vascular dysfunction such as epidural venous engorgement and bleeding [13]. Compression of the thecal sac could be clearly demonstrated on MRI images. A typical feature could be found on axial MRI images, where the overgrowth adipose tissue results in circumferential compression of the thecal sac, referred to as the "Y-sign" or "Stellate-sign" [14]. Epidural adipose tissue that has a thickness greater than 7 mm has been reported to be the diagnostic criterion for SEL [4,11].
The treatment of SEL depends on the severity of neurologic manifestations. Surgical treatment consisting of decompressive laminectomy with excision of epidural adipose tissue is required in patients who are refractory to the conservative treatment. Prognosis with surgical management looks favorable and no case of recurrence has been reported [15]. Conservative treatment including weaning of steroids and weight loss is recommended for patients without significant neurological deficits. Weight loss has been reported to be beneficial in obese patients [10][11][12]. Non-obese patients not receiving steroids should undergo endocrinological evaluation.
We suggest that SEL should be considered as a differential diagnosis when patients presenting with neurological symptoms have conditions pertaining to hyperinsulinism, may it be obesity or exogenous steroid administration. Early detection of SEL and conservative management including diet and specific insulin resistance treatment might avoid the need for surgical management.