Drs. Segal, Jurkat-Rott, Levitt, and Lehmann-Horn put together an “Owners Manual for Hypokalemic Periodic Paralysis” that seeks to address frequently asked questions by patients and physicians. Please click on the link to access it.
What are the Periodic Paralyses?
First, a simplified blurb on normal physiology:
Nerves are like electric wires that transmit signals from the brain to the muscles. Muscle cells have potassium and sodium on the inside and outside of their cell membranes. Muscle cells respond to nerve signals by letting ions change location from the inside to the outside and from the outside to the inside of their cell membranes. The ions cross the muscle membrane through ION CHANNELS. Each ion (i.e. sodium, potassium, calcium, and chloride) has its own channel.
Periodic paralysis and the non-dystrophic myotonias are diseases where people get muscle weakness and/or muscle stiffness. This happens because the ION CHANNELS in the muscle membrane are faulty. The faulty ion channels prevent the potassium and sodium from being where they need to be. The misplaced ions cause the ion channels to shut off inappropriately, causing weakness, or not to shut off inappropriately, causing stiffness.
Of the periodic paralyses and non-dystrophic myotonias, there are several different disease types that have been identified. A brief description of each disease follows. Please be aware that there are many people with overlapping symptoms (for example, they experience paralysis AND myotonia), there are a wide variety of symptoms that are not listed below, and that many people do not fit the exact mold of the classifications below (for example, acetazolamide does not help all patients with hypokalemic periodic paralysis and indeed can make some patients worse)
Hypokalemic Periodic Paralysis Subtypes:
Genes: Sodium channel, Potassium Channel, Calcium channel
Secondary: Thyroid over-activity
Endocrine or renal problems: Certain substances and medications
Main Symptoms: weakness, low serum potassium; permanent muscle weakness
Main Triggers: carbohydrates, salt, rest after exercise, stress, cold, insulin
Things that Alleviate Attacks Acutely: potassium
Things that Prevent Attacks Chronically: acetazolamide, dichlorphenamide, spironolactone, triamterene, amiloride, proper diet, avoidance of triggers
Hyperkalemic Periodic Paralysis Subtypes
Genes: Sodium channel
Secondary: Renal problems
Main Symptoms: weakness, usually less duration than in hypokalemic periodic paralysis, myotonia (muscle stiffness that can be alleviated by exercise), high serum potassium; permanent muscle weakness
Main Triggers: potassium intake, rest after exercise, stress, hunger, cold
Things that Alleviate Attacks Acutely: Carbohydrates (simple sugars), insulin, albuterol, calcium injection
Things that Prevent Attacks Chronically: acetazolamide, dichlorphenamide, other potassium-wasting diuretics (e.g. hydrochlorothiazide), proper diet, avoidance of triggers
Gene: potassium channel
Definition: Periodic Paralysis (hyper or hypo), long QT syndrome, and skeletal abnormalities (wide spaced eyes, low-set ears, webbed fingers or toes)
Main Symptoms: weakness, palpitations, atypical attacks with muscle twitching (myoclonus); low or high serum potassium (depends on associated periodic paralysis)
Main Triggers: same as that for the type of periodic paralysis they have Things that Alleviate Attacks: same as that for the type of periodic paralysis they have
Things that Prevent Attacks Chronically: same as that for the type of periodic paralysis they have
Gene: sodium channel
Definition: muscle stiffness that worsens with exercise (paradoxical myotonia) and with cold
Main Symptoms: muscle stiffness followed by weakness, especially with exercise in cold weather; can be associated with hyperkalemic periodic paralysis; normal serum potassium; no warm-up phenomenon
Main Triggers: same as those for hyperkalemic periodic paralysis; cooling and heavy muscular work
Things that Alleviate Attacks Acutely: warm environment relieves stiffness, no therapy to relieve weakness acutely; same as for hyperkalemic periodic paralysis (if hyperkalemic periodic paralysis is a feature)
Things that Prevent Attacks Chronically: acetazolamide, mexilitene; same as for hyperkalemic periodic paralysis if that is a feature
Gene: Sodium channel
Main Symptoms: intermittent, generalized muscle stiffness; no weakness; not worsened by cold
Main Triggers: potassium ingestion; rest after exercise; succinylcholine anesthesia
Things that Alleviate Attacks Acutely: same as for hyperkalemic periodic paralysis
Things that Prevent Attacks Chronically: mexiletine, acetazolamide
Gene: Chloride channel
Main Symptoms: muscle stiffness
Main Triggers: sudden exercise, sudden noise
Things that Alleviate Attacks Acutely: repeated movement of stiff muscle (warm-up phenomenon)
Things that Prevent Attacks Chronically: mexilitene, acetazolamide, phenytoin, quinine, carbamazepine
Hypokalemic Periodic Paralysis Frequently Asked Questions (FAQs):
Q. What is Periodic Paralysis?
A. Periodic paralysis is a spectrum of neuromuscular disorders all resulting in episodes of weakness and/or paralysis occurring with variable frequency and lasting anywhere from a few minutes to days. There are two major recognized types of periodic paralysis: that with attacks of weakness caused by high blood levels of potassium, termed HYPERkalemic periodic paralysis, and that with attacks of weakness caused by low blood levels of potassium, termed HYPOkalemic periodic paralysis.
Hypokalemic periodic paralysis can have a number of causes:
- hyperthyroidism, a condition where your thyroid gland makes too much thyroid hormone, can cause hypokalemic periodic paralysis in susceptible patients;
- conditions where your body excretes (gets rid of) too much potassium for a number of reasons;
- a mutation in a gene coding for a calcium channel in your cells arises, causing you to have bouts of weakness. The third condition is called familial hypokalemic periodic paralysis and can be passed down from parent to child.
Q. What causes hypokalemic periodic paralysis?
A. See above
Q. No one in my family has this disease. How did I get it?
A. Say you have a family whose members have hypokalemic periodic paralysis. Say the child has it, the mom has it, and mom’s dad has it, and so on. Somebody in the family, way back when, had to be the first one to get the disease. He or she was unfortunate to get a mutation in the gene that causes this illness. Once one person has gotten the mutated gene, he or she can pass on the gene to future generations. So, if you are the first in your family to get the disease, this is possible. One must be aware that some people can carry the mutated gene, but for one reason or another, do not show signs of illness. So, you may not indeed be the first person in your family with the mutated gene. Then again, maybe you are.
Q. Will I pass this on to my children and how does inheritance work?
A. Many cases of hypokalemic periodic paralysis have been proven to be caused by a mutation in a certain gene called the “DHP-sensitive calcium channel.” Healthy humans have one set of 23 genes from their mother and a corresponding set of 23 genes from their father. So, for the calcium channel gene, any human has two copies, one from mom and one from dad. When someone has a child, they pass on one of the two copies of a gene to their child, and their partner passes on the other copy to their child.
Now, let the good copy of the gene be labeled “g.” Let the bad copy be labelled “G.” Most humans have “g from mom” and “g from dad”. A hypokalemic periodic paralysis patient generally has “G from one parent” and “g from the other parent.” Now, let’s make a grid (called a Punnet square in the world of genetics): Say Mom has hypokalemic periodic paralysis.
Mom can give either the bad copy or the good copy of the gene. Dad can give only a good copy. Their child will have a 50% chance of getting the bad gene and therefore a 50% chance of getting hypokalemic periodic paralysis.
Q. What kinds of things trigger attacks? How can I determine what triggers my attacks?
A. Hypokalemic periodic paralysis patients describe a few triggers that apply to everyone: rest after exercise, high carbohydrate meals (that is, pasta, pizza, cakes, candy, sugar, rice, potatoes, french fries, etc.), and salty foods (that is, table salt, a.k.a. sodium chloride, a.k.a. NaCl).
Other triggers vary from person to person: alcoholic beverages, large meals, Chinese food (perhaps due to MSG), stress, cold weather, high humidity, dehydration, excessive bedrest, accidentally skipping doses of medications, viral illnesses such as the flu, diarrhea, and lack of sleep (this list is not comprehensive).
One method of discovering what triggers your own attacks is to keep a diary. This has proven useful to a number of people with periodic paralysis. You should first establish a grading system for your attacks: for example, mild = 1; moderate = 3; severe = 7; complete = 9.