Annals of Indian Academy of Neurology
  Users Online: 1196 Home | About the Journal | InstructionsCurrent Issue | Back IssuesLogin      Print this page Email this page  Small font size Default font size Increase font size


 
Table of Contents
CASE REPORT
Year : 2014  |  Volume : 17  |  Issue : 1  |  Page : 100-102
 

Reversible electrophysiological abnormalities in hypokalemic paralysis: Case report of two cases


Department of Neurology, Sawai Man Singh Medical College, Jaipur, Rajasthan, India

Date of Submission14-Jun-2013
Date of Decision05-Jul-2013
Date of Acceptance15-Aug-2013
Date of Web Publication12-Mar-2014

Correspondence Address:
Kunal Nath
Department of Neurology, Sawai Man Singh Medical College, Jaipur - 302 004, Rajasthan
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-2327.128566

Rights and Permissions

 

   Abstract 

Compound muscle action potential (CMAP) amplitude declines during a paralytic attack in patients with hypokalemic periodic paralysis (HPP). However, serial motor nerve conduction studies in hypokalemic paralysis have not been commonly reported. We report two cases with hypokalemic paralysis, who had severely reduced CMAPs in all motor nerves at presentation during the episode of quadriparesis. However, the amplitude of CMAPs increased and reached normal levels, as the serum potassium concentration and motor power returned to normal state.


Keywords: Compound muscle action potential, electrophysiology, hypokalemic periodic paralysis, motor conduction abnormalities


How to cite this article:
Sharma C M, Nath K, Parekh J. Reversible electrophysiological abnormalities in hypokalemic paralysis: Case report of two cases. Ann Indian Acad Neurol 2014;17:100-2

How to cite this URL:
Sharma C M, Nath K, Parekh J. Reversible electrophysiological abnormalities in hypokalemic paralysis: Case report of two cases. Ann Indian Acad Neurol [serial online] 2014 [cited 2019 Oct 20];17:100-2. Available from: http://www.annalsofian.org/text.asp?2014/17/1/100/128566



   Introduction Top


Electrophysiological abnormalities reported in hypokalemic periodic paralysis (HPP) include reduced compound muscle action potential (CMAP) amplitude during a paralytic attack, increased CMAP amplitude 5 min after maximal muscle contraction, progressive reduction in amplitude 20-40 min after rest [1] and rarely reduced sensory nerve action potential (SNAP) amplitudes. [2]

Sensory nerve conduction (NC) abnormalities that reversed with hypokalemia correction and improvement in muscle weakness have been reported; [2] however, similar findings in motor NC studies have been uncommonly reported. We report case reports of two patients with reversible motor conduction abnormalities.


   Case Reports Top


Case 1

A 20-year-old girl with no significant past medical illness presented with flaccid are flexic quadriparesis of 2 day duration. She had bulbar and respiratory involvement in form of dysphagia and her single breath count was nine. She also had cranial nerve involvement in form of bilateral facial weakness, neck flexor weakness, and dysphagia. The power in all muscle groups was 1/5. There was no sensory loss, bladder disturbance, or higher function disturbance. She was evaluated for electrolyte abnormalities (suspecting a possible diagnosis of hypokalemic paralysis). The electrocardiography (ECG) showed U waves. Arterial blood gas analysis showed normal pH, normal partial pressures of oxygen and carbon dioxide, and normal bicarbonate levels. Simultaneously, she underwent NC study. The NC study showed significant reduction in CMAP amplitudes of all motor nerves. The distal latencies and conduction velocities were normal in the motor nerves. However, the F-waves were non recordable in all the tested motor nerves. SNAP were also normal. Based on the electrophysiological findings, an alternate diagnosis of acute motor axonal neuropathy (AMAN) form of Guillain-Barre syndrome (GBS) was also considered. In the meantime serum potassium report was available and was 1.9 mmol/L. With administration of potassium (160 meq intravenous over 24 h followed by 60 meq per day in three divided doses orally in form of potassium chloride) patient showed dramatic clinical improvement. Based on this, the original diagnosis of hypokalemic paralysis with quadriparesis with cranial nerve and respiratory involvement was confirmed. NC studies were repeated 24 h after the initial study, by which time patient's motor power was back to normal and serum potassium was 2.9 mmol/L. Repeat NC was found to be normal. The secondary causes of hypokalemia including thyrotoxicosis, renal tubular acidosis, gastrointestinal loss were ruled out (FT3-3.20 pg/mL, FT4-1.10 ng/dL, TSH − 3.80 uIU/mL, arterial pH − 7.45). The short and long duration exercise test to document channelopathy as cause of hypokalemia was planned, but patient did not give consent for the same. As no definite secondary cause of hypokalemia could be found, the patient was not put on any prophylactic therapy. The patient was advised against heavy manual labour and avoiding heavy carbohydrate meals.

Case 2

A 52-year-old male with no past medical illness presented with flaccid areflexic quadriparesis of 1 day duration. There was no sensory loss, cranial nerve involvement, bladder disturbance, or higher function disturbance. The power in upper limb muscle groups was 2/5 and in the lower limb muscle groups was 3/5. The ECG done in the emergency ward showed U waves. He was evaluated for electrolyte abnormalities (suspecting a possible diagnosis of hypokalemic paralysis) and while the reports were still pending, he underwent NC study. The NC study showed significant reduction in CMAP amplitudes of all motor nerves. However, distal latencies and conduction velocities of motor nerves were normal. F-wave latencies were non recordable in all tested motor nerves. SNAP amplitudes were also normal. Based on the electrophysiological findings, an alternate diagnosis of AMAN form of GBS was also considered. The serum potassium report was 2.0 mmol/L. With administration potassium (160 meq intravenous over 24 h followed by 60 meq per day in three divided doses orally in form of potassium chloride), the patient showed dramatic clinical improvement. Based on this, the original diagnosis of hypokalemic paralysis with quadriparesis was confirmed. NC study was repeated 24 h after the initial study, by which time the patient's motor power was back to normal and serum potassium was 3.9 mmol/L. Repeat NC study was found to be normal. The secondary causes of hypokalemia including thyrotoxicosis, renal tubular acidosis, gastrointestinal loss were ruled out (FT3-3.09 pg/mL, FT4-1.03 ng/dL, TSH − 2.90 uIU/mL, arterial pH − 7.4) The short and long duration exercise test to document channelopathy as cause of hypokalemia was planned, but patient did not give consent for the same. As no definite secondary cause of hypokalemia could be found the patient was not put on any prophylactic therapy. The patient was advised against heavy manual labor and avoiding heavy carbohydrate meals.

The NC study report before and after correction of hypokalemia and recovery of muscle power depicting the changes in the CMAP of the motor nerves.

As there was no asymmetry between nerve conduction findings of left and right side, only right-sided nerves are described for sake of convenience [Table 1].
Table 1: Nerve conduction studies

Click here to view



   Discussion Top


Reversible electrophysiological abnormalities of sensory nerve function have been reported earlier. [2] A prospective study in 10 patients with HPP revealed a pattern of reduced sensory action potentials during paralytic attacks, which normalized with correction of serum potassium. The mechanism could be related to the dorsal root ganglia having an incomplete blood-nerve barrier, and neuronal inexcitability was postulated to occur consequent upon possible inactivation of the sodium-potassium pump by the low concentration of extracellular potassium. These authors could not find any abnormalities in the motor nerve function.

In another study on muscle fiber conduction velocity (MFCV) in patients with hypokalemic weakness of various etiologies, Cruz-Martinez and Arpa [3] found inexcitability of most muscle fibers during an acute attack, with associated slowing of MFCV. They also found increased threshold in the axons, consistent with hyperpolarization. Activity-dependent conduction block was induced by voluntary contraction and excitability abnormalities resolved with potassium replacement.

In our patients, the predominant finding on motor conduction studies was the severe reduction in amplitudes of the CMAPs and nonrecordable F-wave latencies. The sensory conduction studies were normal. The most dramatic finding in our study is the progressive improvement in the CMAP amplitudes and normalization of F-wave latencies with the administration of potassium and improvement of motor power, reaching normal levels by 24 h with normalization of motor power.

To our knowledge, there has been only a single case report before this, of motor nerve CMAP amplitude changes in hypokalemic weakness, with serial study showing normalization of the abnormalities with correction of serum potassium. [4] But in that case report, the patient did not have bulbar or respiratory involvement and there were no abnormality in the F-wave latency. Based on published reports, we believe that hypokalemia-induced inactivity of the sodium-K-ATPase leading to inexcitability of muscle fibers underlies the abnormalities detected in our patients. Hyperpolarization of muscle fibers occurs with decreased extracellular potassium concentration, although in severely reduced potassium levels, myofibers paradoxically depolarize to a stable potential of −60 mV from their baseline potential of −85 mV. [5] This results in failure of excitation of muscle fibers by supramaximal stimulation of peripheral nerves, thus resulting in decreased CMAP of the tested nerves. Also during acquired hypokalemic paralysis, there is axonal hyperpolarization, which reverses after serum potassium becomes normal. [6] This could explain the decreased CMAP of peripheral nerves and its recovery after correction of hypokalemia. Such abnormalities are not more often detected in patients presenting with hypokalemic weakness probably because nerve conduction studies are not routinely performed in these patients. This report highlights the fact that NC studies can be misleading in patients presenting with flaccid quadriparesis, especially when there is no reason to suspect hypokalemia. One should suspect a diagnosis of hypokalemic weakness in a patient presenting with NC features of AMAN variant of GBS.

 
   References Top

1.Graves TD, Hanna MG. Neurological channelopathies. Postgrad Med J 2005;81:20-32.  Back to cited text no. 1
    
2.Inshasi JS, Jose VP, van der Merwe CA, Gledhill RF. Dysfunction of sensory nerves during attack of hypokalemic periodic paralysis. Neuromuscul Disord 1999;9:227-31.  Back to cited text no. 2
    
3.Cruz-Martinez A, Arpa J. Muscle fiber conduction velocity in situ in hypokalemic periodic paralysis. Acta Neurol Scand 1997;96:229-35.  Back to cited text no. 3
    
4.Rajshekhar G, Kumar S, Prabhakar S. Reversible electrophysiological abnormalities in hypokalemic periodic paralysis. Indian Pediatr 2008;45:54-5.  Back to cited text no. 4
    
5.Jurkat Rott K, Weber MA, Fauler M, Guo XH, Holzherr BD, Paczulla A, et al. K+dependent paradoxical membrane depolarization and Na+overload, major and reversible contributors to weakness by ion channel leaks. Proc Natl Acad Sci U S A 2009;106:4036-41.  Back to cited text no. 5
    
6.Kuwabara S, Kanai K, Sung JY, Ogawara K, Hattori T, Burke D, et al. Axonal hyperpolarization associated with hypokalemia: Multiple excitability measurements as indicators of membrane potential of human axons. Muscle Nerve 2002;26:283-7.  Back to cited text no. 6
    



 
 
    Tables

  [Table 1]


This article has been cited by
1 A Case Report of Thyrotoxic Periodic Paralysis; Serial Nerve Conduction Studies before and after Recovery
Min Suck Kim,Jung A Park,Jung Im Seok
Korean Journal of Clinical Neurophysiology. 2015; 17(2): 98
[Pubmed] | [DOI]



 

Top
Print this article  Email this article

    

 
   Search
 
  
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Article in PDF (436 KB)
    Citation Manager
    Access Statistics
    Reader Comments
    Email Alert *
    Add to My List *
* Registration required (free)  


    Abstract
   Introduction
   Case Reports
   Discussion
    References
    Article Tables

 Article Access Statistics
    Viewed1708    
    Printed43    
    Emailed0    
    PDF Downloaded85    
    Comments [Add]    
    Cited by others 1    

Recommend this journal