Age and gender
Sixty-six patients aged between 41 and 82 years with a mean age of 60 ± 14 years participated in the survey. The gender was not totally evenly distributed as 30% were male and 70% were female. In the age group above 70 years (9 patients) there were no males.
Genetic and clinical diagnosis
A causative mutation was identified in 14 patients (24%). Seventy percent (70%) of participants were diagnosed as HypoPP, 9% as HyperPP, 6% as paramyotonia congenita (PC), 9% as Andersen syndrome (AS), and 6% were clinically diagnosed as periodic paralysis without specification of a subtype (excerpt of data in ). Sixty-two percent (62%) had a known family history of PP, 24% were unsure of family history, 14% were sporadic cases. Family history was positive in 69% of patients with identified causative mutation and in 60% without an identified mutation and therefore did not influence success of genetic diagnosis.
Data excerpt: comparison of the diagnoses
Age at onset and age at diagnosis
Onset age was before 2 years in 14% and before 20 years in 74%. Only 15% had onset after the age of 30 years. Mean age of onset was 16.8 ± 13.8 years. Median age at which patients were diagnosed was 37.5 years. The mean latency between onset and diagnosis was 26 years. Age at diagnosis was bi-modally distributed with one peak during childhood and a second peak at approximately 40 years. Of the 17 patients diagnosed before age 20, 18% had no previously recognized family history, while 82% were from families with a recognized history of periodic paralysis, pointing to the importance of family awareness for early diagnosis ().
Age at onset of symptoms and age at diagnosis.
The frequency of episodes was weekly in 59%, daily in 28% and not present in 11%. With age, 21% of patients reported decreased frequency, 64% unchanged frequency, 11% increased frequency of weakness episodes while 4% were unsure (or the question did not apply, as they had only had PMW and no paralytic episodes). Likewise with age, 30% reported episodes of less severity, 58% of unchanged severity while 6% were unsure or the question did not apply. No patients reported increased severity of paralytic episodes.
Permanent weakness (PMW)
Sixty-eight percent (68%) reported muscle weakness which is always present and varies little from day-to-day, defined as PMW. Twenty-three percent (23%) were unsure if their weakness was permanent and 9% did not experience PMW. PMW was more prominent in proximal than in distal muscles ().
Distribution of permanent muscle weakness.
Pain, fatigue, and muscle stiffness
In the four weeks prior to the survey, 82% of participants reported experiencing pain, of these, 43% of moderate to severe intensity. Eighty-nine percent (89%) reported fatigue, of these, 66% of moderate to severe intensity. Sixty-seven percent (67%) reported muscle stiffness, of these 59% of moderate to severe intensity.
Incapacitation and injuries
At age 18-35 years, 83% were moderately to very active and 17% mildly active or sedentary; at the time of survey, 14% were moderately to very active and 86% mildly active or sedentary. Incapacitation was reported as follows: 92% had reduced strength and stamina, 89% reported difficulty performing activities of daily living, 89% felt limited in the type of work and activities they are able to do, 75% experienced difficulties with mild exercise, 55% report lack of endurance, 42% could climb only a single flight of stairs, 25% were unable to walk more than a few steps unaided. At the time of survey, 8% of patients reported they have as much strength and stamina as age-matched peers, but most of these individuals simultaneously reported PMW. Based on this, 91% are dissatisfied with what they were able to accomplish.
Sixty-seven percent (67%) reported injuries from falls which were severe enough to require medical attention. These included bruises, sprains, torn ligaments and joint capsules, injuries of cartilage, bone fractures, concussion, and internal bleeding.
Thirty-five percent (35%) of female patients and 33% of male patients reported depression, which three attributed to side effect from carbonic anhydrase inhibitor, specifically acetazolamide (). Patients expressed reluctance to discuss their depression with their physicians and may need reassurance that depression is often a consequence of chronic illness.
Mobility aids and
Forty-nine percent (49%) of patients use one or more mobility aids: 17% use a walker, 20% use a scooter, 23% use a wheelchair, 29% use a cane, 26% use other aids. In addition to mobility aids, patients employ a number of strategies to compensate for their handicap. These include: careful pacing of activity level and the use of appliances and devices to reduce physical effort, avoiding repetitive or unnecessary movement, resting when needed, using accessory muscle groups, and arranging or asking for help.
Professional physiotherapy versus self-managed exercise
Fifty-seven percent (57%) of participants have had professional physiotherapy. Of these, 49% experienced significant or mild benefit, 40% deterioration and 11% no change. Eighty-three percent (83%) of participants reported to have followed self-directed programs of exercise, of these, 62% experienced significant or mild benefit, 16% deterioration, and 22% no change ().
Benefit of professional physiotherapy versus self-managed exercise.
The types of exercise differed little whether physiotherapy or self-directed, it was rather the intensity, frequency and duration of the sessions which differed. Patients who experienced increased weakness with physiotherapy made these representative comments; "Physiotherapist pushed me to use all my strength, work to the point of fatigue, accelerated the level of activity too quickly, and made me worse," "...triggered episodes of myotonia and made me worse," "I could manage at the start, but within a few weeks, I would get demonstrably weaker."
To detect possible gender-specific effects, we performed subgroup analysis of males and females. There are tendencies for a differing distribution of muscle weakness, with males reporting more weakness in quadriceps muscles and females reporting more weakness of arms, shoulder girdle and neck muscles. Also, females suffered more from pain, fatigue and stiffness than males and deteriorated more severely when undergoing physiotherapy ().
For examining the age-related development of weakness, patients were divided into three age groups: 41-50, 51-60, and 61-82 years. PMW was reported in 65%, 59% and 84% of patients, respectively, mainly due to weakness in quadriceps, hip girdle, and calves. There was a tendency for increased rates of PMW with age for almost all muscle groups except for muscles of trunk, face, and upper extremities which showed somewhat constant rates of PMW. Stiffness decreased in 81%, 68%, 50% of the patients in the respective age groups; whereas age did not affect pain, fatigue, or benefits from physiotherapy and self-managed exercise ().
Age-related development of weakness†.