An MRI spine may be requested for the investigation of an acutely weak leg, but it is not just the cord and exiting nerve roots that one should look at.
We report an unusual case of a 41 year old gentleman with a spontaneous iliacus haematoma causing a compressive femoral neuropathy, as a first presentation of Haemophilia B (Factor IX deficiency).
He presented with acute right groin pain followed closely by right lower limb weakness and sensory disturbance. He had a history of sciatica and a lumbar microdiscectomy 13 years earlier but no personal or family history of abnormal bleeding.
Examination revealed sensorimotor disturbance in the right leg consistent with a femoral mono-neuropathy, with exacerbation of pain in hip extension.
Initial lumbosacral MRI, performed for nerve root entrapment, did not reveal a cause for the patient's symptoms. It was only on further review of the surrounding pelvic structures on the MRI that a haematoma was detected.
Abnormal coagulation studies led to a diagnosis of factor IX deficiency.
He was managed conservatively with replacement of his clotting factors and physiotherapy.
This case nicely illustrates the wide differential diagnosis in an acute mononeuropathy.
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