To raise awareness about the diagnostic value of both cyclic sciatica and the use of MRN for the diagnosis of endometriosis involving peripheral nerves.

Endometriosis prevalence is around 1-7% in young women. Cyclic  sciatica due to endometriosis was first described in 1955. Invasion of the nerve generates pain and motor disorders leaving disability due to external compression, perineural invasion, hemoglobin deposition and release of inflammatory cytokines. The neuropathic pain that at first is cyclic, later becomes chronic and independent of the menstrual cycle. The MR neurography (MRN) helps in its recognition and management decisions.

Description of a clinical case and review of literature.

A 35-year-old female patient consulted for right low back pain extending along her posterior thigh, calf and foot since 2 years. The pain was recurrent, acute in onset, lasted several days and gradually diminished until disappearing. It was refractory to common analgesics and during the crisis she had difficulties to walk.  Neurologist requested a calendar of pain in which the relationship between the menstrual cycle and the pain became evidenced. We performed MRN of the lumbo sacral plexus that showed multiple endometriotic implants in ovaries, L5-S1 roots and a huge one on the sciatic nerve (intra and extrapelvic segment). The patient started oral contraceptives but presented progressive worsening of pain until it became constant and developed steppage. Electromyogram showed acute and chronic axonal damage in the sciatic nerve distribution. Medical treatment was changed to leuprolide acetate. The patient evolved with improvement of ovarian endometriosis but persistence of sciatic nerve lesions, leg pain and weakness up to now. Surgical option was considered.