Thursday, 29 April 2010

Hypokalemic Periodic Paralysis

What is Hypokalemic Periodic Paralysis (HypoKPP) and what are the symptoms?

Hypokalemic Periodic Paralysis is a rare inherited muscle disorder that causes episodes of paralysis or weakness. During severe attacks the patient may become totally unable to move and even appear unconscious. Despite being unable to speak or open their eyes the patient is awake and completely aware of their surroundings during attacks.
Patients with HypoKPP typically begin showing symptoms in the first or second decade of life, often as they enter puberty. About 65% develop symptoms before the age of 16, but first symptoms have been documented in patients as old as 60-70 years. In patients who develop symptoms at a young age attacks may be infrequent at first, but eventually may occur daily.
Episodes may last anywhere from an hour or two to days, and may vary in intensity from episode to episode, with mild localized weakness in a hand, foot, jaw or limbs one time and generalized paralysis the next. Episodes may be accompanied by extreme muscle tenderness and aching or be entirely painless. Patients may also have what are called abortive attacks - fluctuating daily weakness which lasts for extended periods and has even been mistaken for permanent weakness by physicians. This type of weakness becomes more common in patients as they enter their 40s and in some patients abortive episodes may replace paralytic episodes. Patients often find abortive attacks are more disabling than brief episodes of paralysis.
Weakness most commonly affects the muscles of the arms and legs but may affect the trunk as well. Weakness occasionally affects the eyelid muscles (causing droopy lids). In a few patients the muscles involved in breathing and swallowing can be affected during severe episodes. An irregular or weakened heartbeat can occur during episodes as well. Most patients have normal muscle strength between attacks, but muscle tissue is damaged by attacks and this damage may eventually cause permanent weakness in some patients once they reach their 50s and 60s.

What happens to make me weak during episodes?

During episodes of muscle weakness, potassium flows from the bloodstream into muscle cells, affecting the ability of the cell to contract properly. Potassium levels usually fall during attacks but are normal between attacks.

What causes HypoKPP?

All of the periodic paralyses are caused by abnormalities in the ion channels (especially the sodium and calcium channels) of the muscle membrane. The ion channels control the movement of sodium, chloride, potassium and calcium across the cell membrane and from one cell compartment to another. This movement of ions produces the electrical 'spark' which allows our muscles to move. Hypokalemic Periodic Paralysis is caused by a flaw in an ion channel in the muscle membrane. This flaw makes the person with HypoKPP extremely sensitive to decreases in serum potassium that wouldn't bother the average person. Anyone can be made weak by a drastic lowering of serum potassium, but the person with HypoKPP gets weak with even a slight fall in potassium level, and patients with HypoKPP may become profoundly paralyzed while their potassium levels remain within normal limits.

No one in my family has this disease. How did I get it?

In a majority of cases HypoKPP is inherited, but a person may carry, and pass on, the defective gene without ever experiencing any symptoms at all. But some cases just happen, like any other birth defect, for reasons which are unclear.

Will I pass this on to my children and how does inheritance work?

The chances that a child of an affected person will inherit the defective gene is 'statistically' 50%, but not all who inherit the gene will have symptoms. The degree to which children who are affected may vary from one child to the next. One child may be mildly affected, the next seriously affected and the next unaffected. Even identical twins may be affected to different degrees.

“My potassium level is never outside of the normal level yet the doctor says I have Hypokalemic Periodic Paralysis. Why does she call it that? Wouldn't it be better to call it Normokalemic Periodic Paralysis?”

Those with HypoKPP have episodes during which the potassium usually falls. It may only fall by a fraction of a point, and it may never fall below normal, but it usually falls a little. If it does not other criteria may be applied. Those with HypoKPP often respond with an attack of weakness to the administration of carbohydrates (such as a drink of glucose). This weakness disappears when the patient is given potassium, either to drink or by IV. Other simple tests can be applied. In HypoKPP the urine the patient produces during an attack of serious weakness or paralysis can be collected and analyzed. Patients with HypoKPP stop excreting potassium during attacks. This is probably because so much of the potassium in the blood moves into the muscle cell during episodes. Patients with NormoKPP usually react with an attack of weakness to potassium administration. Genetically some cases of so-called ‘NormoKPP’ have now been proven to be a variant of HyperKPP.

What triggers attacks?

Many episodes of weakness are triggered by food. Food triggers include sweet or sugary foods or starchy foods. These are foods like candy, cakes, desserts, soft drinks which are sweetened with sugar, fruit juices, bread, cereal products, rice, potatoes, and pasta. Foods like these are processed by the body very quickly and raise the blood sugar rapidly. The pancreas responds to this rapid rise in blood sugar by producing a lot of insulin. Insulin drives potassium from the blood into the cell, which triggers weakness. Salty foods, like burgers or potato chips, are a trigger for many HypoKPP patients. Getting too hungry, or eating a large meal (especially if you are very hungry) triggers episodes in many patients.
Other common triggers include unusual activity or exercise - usually the day before the attack, but sitting still for too long may also trigger episodes. Patients learn that pacing their activities is absolutely vital to gaining control. Sleep is a potent trigger, and many patients wake up paralyzed. Getting too cold (or too hot) makes some patients weak. Weather changes trigger episodes in some patients.
Many commonly prescribed medications may cause paralysis. These include muscle relaxants and beta-blockers, some types of tranquilizers, analgesics (pain killers), antihistamines, the puffers used to treat asthma attacks, some antibiotics and cough syrups. The eye drops used to dilate the pupil during eye exams have been reported to cause paralysis. Epinephrine or adrenaline , a drug routinely added to local anesthetics is used as a test to provoke attacks in HypoKPP, so obviously is a drug patients should avoid. Many patients report paralysis attacks occurring in the dentist's chair or in the hours following dental work, or after having a wound stitched or a mole removed.
Over the counter drugs can be dangerous and should be avoided if at all possible. If it is necessary to take something it's wise to begin with 1/4 of the recommended dose to gauge the effect on the muscles.

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