Benign nocturnal alternating hemiplegia of childhood is a rare pediatric neurological condition marked by episodes of weakness on one side of the body that switch sides, mainly during sleep. Children with this condition may have sudden night-time hemiplegia, abnormal eye movements, or brief stiffening spells, and they often wake tired or confused afterward. Symptoms usually begin in infancy or early childhood and can vary in frequency and intensity over time. Most children with benign nocturnal alternating hemiplegia of childhood survive into adulthood, but day-to-day function may be affected by recurrent episodes. Treatment focuses on reducing episodes and improving sleep with medicines and safety measures, and ongoing follow-up with a neurologist is common.
Overview
Benign nocturnal alternating hemiplegia of childhoodSymptoms
Benign nocturnal alternating hemiplegia of childhood causes sudden nighttime episodes of one-sided weakness or paralysis that may switch sides between attacks. Children may have facial droop, slurred speech, or unsteady walking during spells, which resolve after sleep without lasting problems.
Outlook and prognosis
Many living with benign nocturnal alternating hemiplegia of childhood see episodes lessen in frequency and intensity with age, especially after adolescence. Development usually progresses, though some may have mild motor or learning differences that benefit from support. Regular follow-up helps tailor care and reduce nighttime triggers.
Causes and risk factors
Benign nocturnal alternating hemiplegia of childhood likely involves problems in brain signaling, sometimes tied to rare genetic changes. Most cases are sporadic; episodes may be set off by sleep disruption, fever or illness, stress, and sudden temperature or light changes.
Genetic influences
Genetics play a major role in benign nocturnal alternating hemiplegia of childhood. Most cases link to rare, inherited or de novo variants that alter brain ion channels or related pathways. Genetic testing can confirm the cause, guide counseling, and inform family planning.
Diagnosis
Diagnosis centers on a history of recurrent nocturnal hemiplegic episodes, normal exams between attacks, and tests excluding stroke or epilepsy. MRI, EEG, and genetic testing (often ATP1A3) can support the genetic diagnosis of Benign nocturnal alternating hemiplegia of childhood.
Treatment and drugs
Treatment for benign nocturnal alternating hemiplegia of childhood focuses on preventing episodes, easing symptoms during attacks, and supporting development. Care often blends seizure‑style medicines, sleep and trigger management, emergency plans for nighttime events, and therapies such as physiotherapy and speech support. Regular follow‑up helps adjust medications and monitor growth and learning.
Symptoms
Families often notice sudden night-time spells where a child becomes weak on one side, then seems much better after sleep. In Benign nocturnal alternating hemiplegia of childhood, these episodes can switch sides and are closely linked to sleep. Features vary from person to person and can change over time. Early features of Benign nocturnal alternating hemiplegia of childhood may include brief eye movement changes or muscle stiffness before the obvious weakness.
Sudden loss of strength affects one arm and leg, sometimes the face, during a spell. In Benign nocturnal alternating hemiplegia of childhood, walking, grasping, or smiling evenly can be hard until the episode passes. Strength typically returns, especially after sleep.
Spells tend to cluster in the evening or overnight and often stop once the child falls asleep. They can return on waking, sometimes on the opposite side. This sleep pattern is a hallmark of Benign nocturnal alternating hemiplegia of childhood.
The weak side can flip during a spell or between spells. Clinicians call this alternating hemiplegia, which means the side of weakness is not fixed. This shifting pattern can help distinguish it from a stroke.
Rapid, jerky eye movements or eyes pulling to one side can happen before or during an episode. These brief changes can make it hard to focus or track a toy. They are common in Benign nocturnal alternating hemiplegia of childhood.
How people usually first notice Benign nocturnal alternating hemiplegia of childhood?
Families often notice the first signs of benign nocturnal alternating hemiplegia of childhood when a baby or young child wakes from sleep with sudden weakness or paralysis on one side of the body, which then resolves, only to recur on the opposite side on another night. Episodes tend to happen during or after sleep and can look like a stroke, with a floppy arm or leg and sometimes facial droop, but between spells the child usually seems back to baseline. Because these events are frightening and repeat, caregivers typically seek urgent care, and doctors start considering how benign nocturnal alternating hemiplegia of childhood is first noticed by tracking the sleep-linked, side-switching pattern over time.
Types of Benign nocturnal alternating hemiplegia of childhood
Benign nocturnal alternating hemiplegia of childhood is considered a rare, genetic/congenital neurological condition. Variants are defined by the underlying gene involved and whether the change is inherited or occurs for the first time in the child. These variants can influence when symptoms start, how often episodes happen, and whether there are additional features between episodes. Not everyone will experience every type.
ATP1A3-related
This variant involves changes in the ATP1A3 gene, which can shape episode frequency and severity. Some children have earlier onset and more frequent nighttime attacks, with occasional movement or balance issues between episodes. Doctors sometimes classify symptoms as episodic versus between-episode features.
SCN4A-related
Changes in the SCN4A gene can lead to hemiplegic episodes that may include muscle stiffness or floppiness, especially around sleep. Symptoms can fluctuate with fever or exertion, and attacks often improve as the child wakes. The balance of symptoms can shift over time.
Inheritance pattern
Some families show autosomal dominant inheritance, where a parent also carries the variant, while others have a new (de novo) change in the child. Inherited forms can cluster across generations, and onset and episode pattern can vary even within a family. People may notice different sets of symptoms depending on their situation.
Unresolved genetics
In a subset of children, no specific gene change is identified with current testing. Clinical features still fit benign nocturnal alternating hemiplegia of childhood, and management focuses on patterns of episodes and triggers. Learning about types of benign nocturnal alternating hemiplegia of childhood can guide genetic testing and support.
What genetics can tell you about symptoms
Certain ATP1A3 gene variants can trigger nighttime attacks where one side of the body becomes weak or paralyzed, then switches sides between episodes. These variants also link to eye movement problems, brief breathing pauses, and developmental delays in some children.
Causes and risk factors
Most cases stem from a change in a brain-signal gene called ATP1A3, and the change usually arises new in the child. Doctors distinguish between risk factors you can change and those you can’t. Benign nocturnal alternating hemiplegia of childhood often starts in infancy or early childhood. Early symptoms of benign nocturnal alternating hemiplegia of childhood can follow fever, temperature changes, bright light, strong emotions, or poor sleep. Family history is uncommon, but steady sleep, stress control, and avoiding known triggers may lower the chance of episodes.
Environmental and biological risk factors
Families often wonder what inside a child’s body or in their surroundings might raise the chance of benign nocturnal alternating hemiplegia of childhood. Most cases start in infancy and appear without a clear pregnancy or birth trigger. Researchers are still exploring how outside influences interact with our inner biology. Below are the environmental and biological factors currently understood.
Onset in infancy suggests differences in brain circuits present from early development. These biological features may raise the likelihood of benign nocturnal alternating hemiplegia of childhood.
Serious problems during pregnancy or delivery have not been consistently linked. Most children with the condition were born after routine pregnancies and uncomplicated births.
Common childhood infections do not cause the condition, but they can make early symptoms of benign nocturnal alternating hemiplegia of childhood more noticeable. This likely reflects extra stress on developing brain networks.
Episodes often happen at night or around changes in the sleep–wake cycle. These transitions do not create benign nocturnal alternating hemiplegia of childhood but can unmask symptoms in children who are already vulnerable.
Genetic risk factors
The genetic causes of Benign nocturnal alternating hemiplegia of childhood most often involve a single-letter change in a gene that helps nerve cells reset after activity. The main gene is ATP1A3; rarer cases involve ATP1A2. These changes are usually new in the child rather than inherited, though they can be passed on in an autosomal dominant way. Risk is not destiny—it varies widely between individuals.
ATP1A3 variants: Changes in this gene disrupt a sodium-potassium pump that nerve cells use to recover after firing. They explain most cases diagnosed with Benign nocturnal alternating hemiplegia of childhood. Different variants can lead to different symptom patterns.
ATP1A2 variants: Far less often, a similar pump gene is involved. These cases may overlap with hemiplegic migraine in some families. Genetic counseling can help clarify risks for relatives.
Autosomal dominant pattern: A parent with a disease-causing variant has a 50% chance of passing it to each child. Severity and features can vary widely, even within the same family. Family history may be absent if the change first occurred in the child.
De novo changes: In most children, the variant arose for the first time in the egg or sperm or very early after conception. This helps explain why many families have no prior history of Benign nocturnal alternating hemiplegia of childhood. Recurrence risk is usually low but not zero.
Parental mosaicism: Sometimes a parent carries the variant in only a portion of their egg or sperm cells. This can raise the chance of having another child with Benign nocturnal alternating hemiplegia of childhood. Specialized testing may be discussed when planning future pregnancies.
Variable expression: The same genetic change can cause different symptom patterns and intensity. Some children mostly have night-time episodes, while others have broader neurologic features. This variability can make early diagnosis challenging.
Lifestyle risk factors
Lifestyle habits do not cause Benign nocturnal alternating hemiplegia of childhood, but they can influence episode frequency, severity, and recovery. Understanding how lifestyle affects Benign nocturnal alternating hemiplegia of childhood helps families reduce avoidable triggers. The elements below focus on lifestyle risk factors for Benign nocturnal alternating hemiplegia of childhood and ways to modify them.
Irregular or insufficient sleep can precipitate nocturnal hemiplegic episodes. A consistent, early bedtime and calming routine may reduce nighttime attacks.
Vigorous or prolonged activity can trigger hemiplegia or dystonia later that night. Gentle, paced exercise with rest breaks may support motor skills without provoking episodes.
Emotional stress, anxiety, or sudden excitement can set off attacks. Daily relaxation practices and predictable routines may lower episode risk.
Viral illnesses and fever often increase episode frequency and severity. Prompt fever control, hydration, and rest during sickness can blunt attacks.
Risk prevention
Many families want to know how to prevent night-time weakness episodes and keep kids steady day to day. True prevention of the disorder isn’t possible, but you can lower the chance of episodes and reduce their impact. Knowing early symptoms of Benign nocturnal alternating hemiplegia of childhood and common triggers helps you respond before an episode escalates. Prevention is about lowering risk, not eliminating it completely.
A consistent bedtime and wake time can lower night-time episode risk. Keep the room cool, quiet, and dark to support deep, uninterrupted sleep.
Keep a simple diary of meals, activities, stress, illness, and sleep before episodes. Spotting patterns helps you avoid known triggers and plan calmer evenings.
Treat fevers promptly and keep up with routine vaccines to reduce stress on the nervous system. Hydration and rest during colds can also reduce episode likelihood.
Avoid overheating from heavy blankets or over-warm rooms at night. Dress in breathable layers and keep a fan or ventilation as needed.
Transmission
Benign nocturnal alternating hemiplegia of childhood is not contagious—you can’t catch it from someone, and you can’t pass it to others through everyday contact, coughing, or blood. In most children, it results from a new change in a single gene that appears for the first time in the child, so the parents typically don’t have the change and the chance of it happening again in another pregnancy is low, though not zero. Less often, Benign nocturnal alternating hemiplegia of childhood is inherited in an autosomal dominant way, meaning a parent with the gene change has a 50% chance to pass it to each child. A genetics team can explain the genetic transmission of Benign nocturnal alternating hemiplegia of childhood and discuss whether testing for the child and parents makes sense.
When to test your genes
Benign nocturnal alternating hemiplegia of childhood is rare; consider genetic testing when infants or children have recurrent nighttime episodes of one-sided weakness that switch sides, resolve by morning, or follow a consistent pattern. Testing helps confirm the diagnosis, guide care, and avoid unnecessary treatments. Discuss timing with a pediatric neurologist or genetic counselor.
Diagnosis
For many families, the first clues come from repeated night-time episodes of sudden weakness that switch sides and then fade after sleep. Doctors usually begin by looking for this pattern over time and ruling out more common causes like seizures or stroke-like events. Often, the genetic diagnosis of Benign nocturnal alternating hemiplegia of childhood is confirmed with a targeted test when the clinical picture fits. Some diagnoses are clear after a single visit, while others take more time.
Providers look for recurrent episodes of one-sided weakness that may alternate sides and cluster around sleep. Improvement after sleep and onset in early childhood support the diagnosis.
Many episodes ease or stop after a period of sleep. This sleep-related improvement is a hallmark feature doctors watch for during evaluation.
Between episodes, the exam is often near baseline, which helps separate this condition from continuous weakness. During an episode, your doctor documents which side is affected and any associated movements.
Short phone videos of attacks can capture side switching, eye or limb movements, and recovery. These real-world clips help your clinician see details that may not happen in clinic.
Stages of Benign nocturnal alternating hemiplegia of childhood
Benign nocturnal alternating hemiplegia of childhood does not have defined progression stages. It tends to come and go in nighttime episodes with symptom‑free periods in between, so it doesn’t follow a steady, predictable worsening; early symptoms of benign nocturnal alternating hemiplegia of childhood can be hard to spot because they often happen during sleep. Doctors usually start with a conversation about what the episodes look like, when they occur, how long they last, and whether anything seems to trigger them, and may review home videos or sleep‑time observations. Tests are used to rule out other causes (such as seizure disorders), and some teams may suggest genetic testing to look for known changes that fit this pattern; keeping a simple diary of timing and features can also help track it over time.
Outlook and prognosis
Nighttime episodes can be scary and disruptive, especially when a child wakes weak on one side and the pattern switches from night to night. The outlook is not the same for everyone, but many children with Benign nocturnal alternating hemiplegia of childhood (BNAHC) see episodes lessen over time. Early symptoms of Benign nocturnal alternating hemiplegia of childhood often peak in early childhood and tend to improve as the brain matures, though some kids continue to have intermittent spells into adolescence. Day-to-day, families may learn to adjust bedtime routines, track triggers like illness or poor sleep, and plan for a calm recovery window the morning after an event.
Prognosis refers to how a condition tends to change or stabilize over time. For BNAHC, long-term development is usually good: most children have normal intelligence, grow well, and do not have ongoing weakness between episodes. Serious complications are uncommon, and mortality linked directly to BNAHC is not expected in published descriptions, though any prolonged episode with breathing trouble warrants urgent care. Many people find that symptoms become shorter, less frequent, or lighter in intensity as school years progress.
Looking at the long-term picture can be helpful. Keeping regular sleep schedules, treating fevers promptly, and having a plan for nighttime events can reduce impact on family life. Talk with your doctor about what your personal outlook might look like, including how often to review progress and whether any medicines or therapies are worth trying. With ongoing care, many people maintain typical activities, including school, sports with supervision, and independent adult life.
Long-term effects
People living with nighttime episodes often wonder what life will look like years from now. For most, the long-term picture is steady and reassuring, with fewer nighttime attacks and normal growth between them. Long-term effects vary widely, but many families see a clear easing of episodes over time. Benign nocturnal alternating hemiplegia of childhood tends not to shorten life or limit independence for those with otherwise typical development.
Nighttime weakness episodes often become less frequent and milder over the years. Many see long gaps without attacks as adolescence approaches.
Most children keep up with milestones and school skills over time. Lasting changes in movement, speech, or learning are uncommon.
Between episodes, strength and movement usually return to baseline. Doctors often describe these as long-term effects or chronic outcomes.
Events tend to stay tied to sleep or overnight hours across childhood. Daytime functioning is generally normal once an episode passes.
How is it to live with Benign nocturnal alternating hemiplegia of childhood?
Living with benign nocturnal alternating hemiplegia of childhood can mean unpredictable nighttime episodes where one side of the body suddenly becomes weak or briefly paralyzed, then switches sides on another night, while daytime may feel mostly typical. Families often learn to keep routines calm in the evening, plan for safety during episodes, and communicate with schools and caregivers about what to do if weakness appears after sleep or naps. For many, the uncertainty is the hardest part, but having a clear plan, tracking patterns, and regular follow-up with clinicians helps restore a sense of control and eases worry for parents and siblings.
Treatment and drugs
Treatment for Benign nocturnal alternating hemiplegia of childhood focuses on easing attacks, improving sleep, and supporting development over time. Although living with Benign nocturnal alternating hemiplegia of childhood can feel overwhelming, many people manage their symptoms and live fulfilling lives. Doctors may use medicines that calm abnormal brain activity, such as certain anti-seizure drugs, muscle relaxants, or benzodiazepines during episodes; melatonin or other sleep aids are sometimes tried to reduce nighttime events, and a doctor may adjust your dose to balance benefits and side effects. Rescue plans for sudden weakness can include quick-acting medicines, gentle positioning, hydration, and reducing triggers like illness, stress, or sleep loss, while physical, occupational, and speech therapy help maintain strength, coordination, and skills between episodes. Regular follow-up with a neurologist, individualized school supports, and monitoring for anxiety, learning differences, or sleep problems round out care, and research is ongoing into targeted therapies for genetic forms.
Non-drug treatment
For Benign nocturnal alternating hemiplegia of childhood, non-drug care focuses on preventing attacks, shortening episodes, and supporting development between them. Alongside medicines, non-drug therapies can help many families steady day-to-day life and reduce disruptions. Plans are individual and may change as children grow. Early symptoms of Benign nocturnal alternating hemiplegia of childhood can be subtle, so simple routines and tracking often guide what works best.
A steady bedtime and wake time can reduce attacks overnight and after naps. A calm wind-down with dim lights and quiet helps the brain settle.
Falling asleep can quickly ease an episode for many children with Benign nocturnal alternating hemiplegia of childhood. Keep a safe, quiet space ready so a nap can start promptly.
Keep a diary of possible triggers like heat, excitement, or illness and note what happened before each spell. Early symptoms of Benign nocturnal alternating hemiplegia of childhood—like eye movements or sudden fatigue—can signal it’s time to rest or cool down.
Gentle, regular movement helps maintain strength, balance, and joint range. A pediatric physiotherapist can tailor home exercises for days with and without symptoms.
Your genes may have an impact on how drugs work for you
Some medicines for benign nocturnal alternating hemiplegia of childhood can work differently depending on a child’s genetic makeup, which affects how the body processes and responds to drugs. Genetic testing may guide dose choices or medication selection to improve safety and benefit.
Pharmacological treatments
Treatment aims to reduce how often night-time weakness episodes happen and how strong they feel, and to steady sleep. The best-studied option is flunarizine; other medicines are chosen based on symptoms, sleep patterns, and whether seizures are also present. Not everyone responds to the same medication in the same way. Keeping track of early symptoms of Benign nocturnal alternating hemiplegia of childhood and any triggers can help fine-tune choices over time.
Taken daily to lower attack frequency and intensity, especially at night. It can cause sleepiness, weight gain, or ankle swelling, and access may vary by country. First-line medications are those doctors usually try first, based on safety and evidence.
Clonazepam or diazepam may help settle prolonged episodes or ease severe stiffness and improve sleep continuity. They can cause drowsiness and dependence with regular use, so doctors often reserve them for rescue or short-term support.
Evening dosing can help align sleep timing and reduce overnight arousals that may trigger spells. It is generally well tolerated, with occasional morning grogginess or vivid dreams.
This calcium channel blocker is sometimes tried when flunarizine is not available or not effective. Benefits vary, and monitoring for low blood pressure, slow heart rate, or constipation is important.
Genetic influences
Genetics likely plays a role in Benign nocturnal alternating hemiplegia of childhood (BNAHC), but the picture is still emerging. In the related condition called alternating hemiplegia of childhood, many children have a change in a gene called ATP1A3 that often arises for the first time in the child rather than being inherited. In BNAHC, some children may have similar gene findings, while many will have no known gene change on today’s tests, suggesting there may be additional, not-yet-identified causes. Having a gene change doesn’t always mean you will develop the condition. Family history can still be a helpful clue, and doctors may look for known genes tied to hemiplegia and hemiplegic migraine when deciding which tests to order. When available, genetic testing for Benign nocturnal alternating hemiplegia of childhood is typically paired with genetic counseling to explain results, confirm the diagnosis, and discuss the chance of BNAHC or related symptoms in future pregnancies.
Is Benign nocturnal alternating hemiplegia of childhood genetic?
Genetics play a major role in benign nocturnal alternating hemiplegia of childhood. Most cases link to rare, inherited or de novo variants that alter brain ion channels or related pathways. Genetic testing can confirm the cause, guide counseling, and inform family planning.
Pharmacogenetics—how genetics influence drug effects
Families sometimes find that a medicine eases night-time episodes for one child but offers little relief for another. In Benign nocturnal alternating hemiplegia of childhood, genetics likely contribute to this variability, yet no single gene result currently points to a specific, proven drug or dose. Genes can influence how quickly you process certain anti-seizure or calming medicines that may be used to shorten episodes or improve sleep. For example, differences in a liver enzyme called CYP2C19 can change how the body handles clobazam or diazepam, so people who break these drugs down slowly may need lower doses to avoid excessive sedation, while fast metabolizers may require careful dose adjustments to see benefit.
When seizure medicines are considered, well-established genetic checks can improve safety: testing for HLA-B*15:02 in many people with East or South Asian ancestry before carbamazepine, and reviewing CYP2C9 status for phenytoin, can reduce the risk of serious reactions. Some teams also avoid valproate in those with known harmful changes in the POLG gene because of a higher risk of liver and metabolic complications. Overall, pharmacogenetic testing for Benign nocturnal alternating hemiplegia of childhood is best used as supportive information alongside clinical judgment to help choose and dose medications thoughtfully. Age, other medicines, and liver or kidney health still play a major role in how treatments work and what side effects appear.
Interactions with other conditions
Day to day, if a child with Benign nocturnal alternating hemiplegia of childhood also has seizures or migraine, families may notice the nighttime spells come more often or are harder to sort out. Doctors call it a “comorbidity” when two conditions occur together. Early symptoms of Benign nocturnal alternating hemiplegia of childhood can overlap with seizures or migraine auras, so having both can complicate recognition and delay the right treatment during an episode. Sleep issues—whether irregular schedules, insomnia, or sleep-disordered breathing—may intensify nocturnal attacks, and treating sleep problems can sometimes reduce episode frequency. Fevers and common infections can also “exacerbate” (make worse) the weakness spells, so preventive care and prompt fever control are helpful. There is genetic overlap between this condition and other ATP1A3-related neurologic syndromes, which helps explain why some children are later found to have movement symptoms or migraine alongside their hemiplegic episodes.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
History
Throughout history, people have described children who suddenly could not move one side of the body, then later switched sides, only to wake up better after sleep. Families told stories of night-time spells that puzzled doctors and faded by morning, returning days or weeks later. These early accounts hinted at a pattern that would later be recognized as benign nocturnal alternating hemiplegia of childhood.
First described in the medical literature as unusual, sleep-linked episodes of weakness in otherwise healthy children, the condition was initially pieced together from bedside observations and family notes. Doctors noticed that the episodes tended to alternate sides and that sleep often brought relief, a clue that set it apart from strokes, seizures, or infections. Over time, descriptions became more consistent, and case series helped define what many living with benign nocturnal alternating hemiplegia of childhood experience: sudden, shifting weakness that improves after rest, with normal growth between episodes.
In recent decades, awareness has grown as pediatric neurologists compared cases across clinics and countries. Better home video and careful diaries from caregivers made the pattern clearer and reduced misdiagnosis. Some children were once worked up repeatedly for stroke or epilepsy before the alternating, night-linked nature was recognized. As medical science evolved, classification sharpened the boundaries—highlighting that episodes start in childhood, alternate sides, spare consciousness in many cases, and often respond to sleep.
Advances in genetics added another layer. While the condition remains defined by its clinical pattern, research into ion channels—the tiny proteins that help nerve cells send signals—offered possible explanations for why sleep can “reset” symptoms for some. These studies also helped distinguish benign nocturnal alternating hemiplegia of childhood from other pediatric disorders with weakness or movement problems, guiding more focused care plans.
Understanding the history of benign nocturnal alternating hemiplegia of childhood matters because it explains today’s approach: careful tracking of early symptoms of benign nocturnal alternating hemiplegia of childhood, attention to what triggers or eases episodes, and the reassuring observation that many children return to their usual selves after sleep. Not every early description was complete, yet together they built the foundation of today’s knowledge. As clinics share data and long-term follow-up grows, the picture continues to refine—still grounded in what families and clinicians first noticed at the bedside: alternating weakness at night that improves with rest.