A 32 year old woman presents with worsening lower back pain, difficulty in walking and weakness of both lower limbs for 6 months. The pain was severe, exacerbated by activity and poorly responsive to analgesics. The lower limb weakness was pronounced when climbing stairs and getting up from chairs. She also complains of a dry mouth, constipation and urinary frequency. Serum electrolyte levels are normal, while her ESR is 10 mm/1h.
The initial compound muscle action potential amplitude in the deep peroneal nerve was low while repetitive stimulation of the nerve showed an initial decremental response followed by an incremental response of >100% after brief exercise.
P/Q type VGCC antibodies : positive Ach receptor antibodies: negative
No abnormalities are noted.
The CT scan of the chest appears normal.