Alert prescribing physicians not to assume plasma-exchange (PLEX)-responsive CIDP will respond to efgartigimod.

A 43-year-old female developed subacute onset quadriparesis with gait difficulties, progressively worsening over 3-4 weeks. Examination demonstrated proximal and distal upper and lower limb weakness, global areflexia, and length-dependent sensory loss in a stocking-glove distribution. Electromyography displayed diffuse sensorimotor polyradiculoneuropathy with non-uniform demyelinating features fulfilling EAN/PNS criteria. CSF profile showed elevated protein 105 mg/dL (N: < 35 mg/dL) but was otherwise unremarkable. Paranodal antibody testing was negative. Neurofilament light chain was normal (7 pg/ml).  She was started on IVIG 2 g/kg over 5 days followed by 1 g/kg every 3 weeks with partial responsiveness initially (INCAT 8 to 3) but relapsed after the third dose (INCAT 6). IV methylprednisolone was added with no benefit. She was switched to PLEX twice weekly with symptom improvement (INCAT 2). Subsequently, she was switched to efgartigomod PH20 1000 mg weekly; PLEX was abruptly discontinued. After 3 weeks on efgartigimod, she gradually became weaker until she was completely disabled requiring hospitalization. PLEX was reinitiated and Cellcept was added. After six months of treatment with PLEX twice weekly, methylprednisolone IV 500 mg weekly and Cellcept 1000 mg twice daily, she returned to work as a police officer with complete independence (INCAT 1). Currently, she is being tapered with PLEX scheduled on an alternating basis—twice weekly one week & once weekly the next—and methylprednisolone reduced to 500 mg biweekly.

It is unknown which CIDP patients will respond to efgartigimod. Although neonatal FcRn blockers have been deemed a chemical form of PLEX, their efficacy and speed to achieve clinical effect in refractory CIDP may not be equal to plasmapheresis. Furthermore, the exact dosage of efgartigimod in patients undergoing concomitant PLEX has not been established.  We recommend close monitoring of patients undergoing PLEX-efgartigimod transition.