Case Study of the Week: Hypokalemic Periodic Paralysis

Don't you love making a rare diagnosis?  Pinpointing a rare disease is a big win as a nurse practitioner.  First of all, it's simply interesting to see a less common medical condition firsthand rather than buried in a textbook collecting dust on your self.  Secondly, patients with unusual medical conditions are often initially misdiagnosed understandably causing frustration of patients and providers.  You've truly made a difference if you are able to make a rare diagnosis.

The other day in the ER I diagnosed Hypokalemic Periodic Paralysis in a patient for the first time.  Really, it was an accident.  I ordered lab work on this particular individual hoping it would give me some insight into this usually healthy patient's symptoms.  I was rewarded with an answer- an incredibly low potassium level.  I didn't learn about Hypokalemic Periodic Paralysis in nursing school and was assisted in my diagnosis by my physician coworker.  So, to increase my own understanding of this disease I have selected it for this week's case study

Case Presentation

An 18 year old male presents to your emergency department stating he is unable to move his legs.  He has had one similar prior episode of severe lower extremity weakness which resolved spontaneously after a few hours.  This episode has persisted for the past eight hours at which point he decided to seek treatment.  The patient reports recent stress but denies fever, headache and other symptoms of illness.  The patient's vital signs are all within normal limits, he is not taking any medications and has no prior medical history. 

On exam you note significant weakness in the patient's lower extremities although sensation is normal.  The patient is unable to ambulate related to weakness.  Upper extremities are spared.  You order blood work to assist in your diagnosis and note the patient's potassium level is low at 2.0 mEq/L.  Noting the low potassium level you also order an EKG to monitor for arrhythmia.  You observe classic EKG changes of hypokalemia including U waves, flat T waves and ST depression.  Based on this patient's lab values and symptoms, you diagnose him with Hypokalemic Periodic Paralysis. 

Management and Outcome

The preferred treatment of Hypokalemic Periodic Paralysis is oral potassium supplementation.  A 40-60 mEq potassium tablet will typically raise potassium level by 1.0-1.5 mEq/L.  Up to 100 mEq of oral potassium can be given but after this amount repeat potassium levels should be drawn prior to administering further potassium supplementation.  No more than 200 mEq of potassium should be given in a 24 hour period. 

In patients where low potassium levels are causing arrhythmia or airway compromise, IV potassium can be administered.  10 mEq of potassium can be given at a time in 20-60 minute intervals to avoid hyperkalemia.  These patients must be placed on continuous ECG monitoring. 

In patients with frequent attacks of Hypokalemic Periodic Paralysis (HPP) prophylactic medications can be considered.  Carbonic anhydrase inhibitors including acetazolamide (Doamox) and dichlorphenamide (Daranide) are usually effective. 

Sweet and salty foods have been shown to precipitate attacks of HPP.  A low-sodium, low- carbohydrate diet can help prevent attacks. 

Discussion

Hypokalemic Periodic Paralysis is a rare genetic disorder causing a defect in ion channels of muscle cells.  Potassium moves from the blood into the muscle cells making the muscle cell unable to contract regularly.  This results in weakness.  Most commonly patients with HPP experience attacks of weakness in the legs and arms.  These attacks can last hours to days usually resolving within 72 hours.  Attacks range in severity.  Some attacks are painless where others cause tenderness and aching in the affected extremities. 

HPP typically presents between the ages of 10 and 14.  As patients with HPP age the frequency of attacks usually decreases.  Most individuals don't have attacks after the age of 40.  Muscle strength usually resolves completely between attacks but some patients do develop permanent weakness especially as they get older.  

HHP can be difficult to diagnose as it doesn't always cause a below normal potassium level.  The potassium level always drops in an attack of HHP but in some people it may not drop below normal.  

Patients with HHP may be able to identify situations that trigger their symptoms helping to avoid attacks.  Common triggers include exercise,  eating sweet or starchy foods, getting too hungry or eating a large meal.  Patients should be encouraged to identify their triggers so they can control their symptoms as much as possible.

It is important that nurse practitioners are aware of Hypokalemic Periodic Paralysis as it can be difficult to diagnose.  They should consider it as a differential diagnosis in patients presenting with sudden onset of weakness, especially in adolescents. 

 

You Might Also Like: Horse or Zebra? Determining if You are Making a Rare Diagnosis

Comments

The majority of this is on point, great job for catching the diagnosis. Quick release potassium is essential for pulling out of an attack and taking more than 200mEq on a bad day is not uncommon for myself or my mother. On good days no potassium is even needed. Both my levels and my mother's levels are on the low end of normal during routine blood tests but the chance of actually being in a doctor's office to have a blood test done during an attack would be close to impossible to plan since the attacks are nearly immpossible to predict. My symptoms didn't begin to show severity until about the age of 25, looking back I can see issues I've dealt with loosely throughout my adolescents and my mother was the same. I can now see small glimpses of this disease in my daughter and hope she enjoys a wonderful childhood before this awful disease starts manifesting in its full form.

Katrina L

I have had them, most all my life, since I was a child, the heat and cold would trigger it. my mother and older sister had it too. still today at 70 yrs old, I get a little stiff and find it hard to get around some days. my potassium used to go way down when I used to get it.

jackie c

All I can say is she is one smart NP !! Nobody I ever talk to has heard of it...good job. ;-)

Stephanie Gerlach

I am adult with Hypokalemic Periodic Paralysis who also has family members with Hypokalemic Periodic Paralysis. We definitely still have paralysis attacks after age 40. My mother was actually a bit odd and her first major full body paralysis attacks starting at age 47. Prior to that she had occasional weakness throughout her life where her fellow nurses had to temporarily take over for her until she recovered. I had my first full body paralysis attacks at 21 years old, but I had weird short term (5 minutes to 30 minutes) weakness problems from as young as 5 years old.

All the people with Hypokalemic Periodic Paralysis in my family rarely have our Potassium drop below 3.5 K+, but it is usually 3.5K+ to 4.2K+ and and small drop in Potassium level trigger our attacks.

Cold is a major trigger for us all and a standard trigger for the majority of people with Hypokalemic Periodic Paralysis. The cold of an ER when just wearing a hospital gown always makes me much worse causing me to switch back and forth from spasms and paralysis. I always have my family request as many blankets as they can get from the Nursing staff to help lower how much the Cold is making me worse.

I have a positive CMAP Exercise Test as well as a Clinical Diagnosis.

Miriam