Abstract Details

Reduced Compound Muscle Action Potential (CMAP) on Nerve conduction velocity (NCV) tests  during paralytic attacks of hypokalemic periodic palsy have been infrequently reported in case reports. However reversible conduction block and non-recordable F waves has not been previously reported. We report a 35 year old male with HPP who had severely reduced CMAPs with conduction block and non-recordable F waves masquerading as GBS like picture that recovered completely on treatment of hypokalemia.

We report a rare case of hypokalemic periodic palsy (HPP) masquerading as Guillaine Barrè syndrome (GBS).

A 35 year old male,labourer by occupation presented with weakness of all four limbs after getting up in the morning.Weakness was not associated with sensory,bladder, bowel, and cranial nerve involvement. No history of antecedent diarrhea or URI was reported.Power was 1/5 and DTRs were globally absent.Routine blood investigations showed hypokalemia (potassium-2.5 meq/l). ECG showed U waves, NCV test showed reduced CMAPs in all the tested motor nerves with non-recordable F waves and conduction blocks in ulnar, tibial and peroneal nerves with normal distal latencies, conduction velocities, and normal sensory studies.The clinical picture was suggestive of GBS.

The patient was treated for GBS and was started on Intravenous immune globulin (IVIG).  Intravenous potassium chloride was administered for the treatment of hypokalemia.  After 48 hours, the weakness had completely resolved and repeat NCV was normal. IVIG was discontinued, and a diagnosis was of HPP was made. To our knowledge this is the first report of reversible conduction block with non recordable f waves in a patient with HPP.

This report highlights that hypokalemia might masquerade as GBS in NCV testing.Prompt recognition may prevent undue use of expensive IVIG in such cases.