Strubhar, Andrew J. PhD, PT; Meranda, Kathleen MPT; Morgan, Andrew MD
Hypotonia in infancy is an impairment commonly associated with many different pediatric disorders. The disorders associated with hypotonia can be generally categorized by the origin of the pathology. Diseases of the motor unit, genetic and metabolic disorders, as well as central nervous system dysfunction can all be identifiable sources of hypotonia.1 Perhaps the most intriguing and poorly understood group of infants with hypotonia is that in which no definitive cause for the hypotonia is found. In 1957, John Walton used the term “benign congenital hypotonia” (BCH) to classify those with infant-diagnosed hypotonia in which the cause remains unknown.2 Since that time, many definitive causes of hypotonia have been discovered. Yet there remains a group of infants in which the hypotonia appears idiopathic. In many of these children, improvements in the condition are recognized upon follow-up but nonprogressive manifestations persist.3 Other children seem to recover completely. Because there is no known underlying disorder causing the hypotonia, idiopathic hypotonia has been a challenging diagnosis for many physicians and a frustrating one for parents of infants given the diagnosis.
Hypotonia from known conditions, such as Down syndrome, cerebral palsy, spinal muscular atrophy, to name a few, are well understood in regards to prognosis and probable outcomes.4–9 Idiopathic hypotonia, however, is not as well researched and understood in these regards. Parusch et al. indicated that, until recently, many investigators did not follow these children past two years of age.3 Researchers have indeed found that the hypotonia resolves within the first few years in the majority of children with BCH.10 Although it then seems reasonable to assume the child is recovered, some researchers have reported that mild deficits remain. In one study, children diagnosed in infancy with BCH were followed until the end of their third year, and approximately half were found to have minor neurological abnormalities such as hypotonia, clumsy gait, and speech delay.11 Other researchers followed a group of children previously diagnosed with BCH until 12 years of age. These children were also identified as having minor neurological deficits. On the basis of on parental and teacher questionnaires, the researchers found an early diagnosis of hypotonia was related to problems of behavior and motor function, but not to problems in cognition.12 Similar results were found in yet another study of six- to eight-year-old children who had been diagnosed with BCH as infants. They were examined on a variety of sensory, behavioral, and perceptual motor measures and were compared with control children to further clarify prognosis in this population. No significant differences were found between the BCH and control group, except in the area of gross motor performance.3 The results indicated that children with BCH have inferior gross motor performance when they reach school age relative to matched control children.
In a recent study, a consensus was developed among physical therapists and occupational therapists in an attempt to define hypotonia by a collection of characteristics. These characteristics include decreased strength, decreased activity tolerance, decreased motor skill development, round shoulder posture, hypermobile joints, increased flexion, and poor attention and motivation. This consensus recognized both motor and behavioral problems.13 Other investigators have suggested that the motor dysfunction in children with hypotonia may be related to learning, attention, and behavioral deficits.12–18 For example, in one study children five to 11 years old who displayed minor neurological dysfunction, including dysfunctional muscle tone were examined. The researchers found that children with more signs of minimal neurological dysfunction performed worse scholastically and had more signs of attention deficit than others.18
Evidence also exists to suggest a link in familial incidence of BCH. In the study previously cited, past medical records were examined as well as conditions surrounding pregnancy, family history of hypotonia and motor deficits, and other general data regarding the status of the child. The researchers demonstrated a family history of delayed motor achievements in 30% of the cases.11
Information is readily available in regards to differential diagnosis of infant hypotonia.19–22 Likewise, much literature exists describing the outcomes of many of the known causes of hypotonia, such as Down syndrome.4,9 However, research is still lacking in regards to future outcomes of children with idiopathic hypotonia. The early studies previously cited do indicate the presence of some residual problems for the infant diagnosed with idiopathic hypotonia. However, only a handful of investigators describe this group. Likewise, little literature supports any early prognostic indicators for the degree of these residual problems. Thus the aim of this study was to 1) describe the outcomes of children diagnosed with idiopathic hypotonia in infancy, including those with minimal impairments and those whose impairments apparently resolved; 2) compare the outcomes of those with idiopathic hypotonia and those with more global deficits; and 3) determine whether a difference exists between early developmental scores of children with idiopathic hypotonia and those with more global deficits.
To bring clarity to the above purposes, the following operational definitions are used. The term “idiopathic hypotonia” refers to the medical diagnosis assigned to children in infancy. The diagnosis is based on clinical signs such as inappropriate head lag, astasis, and slip-through and, at the time of the diagnosis, the hypotonia is not attributed to or associated with any other condition. Slip-through occurs when a child is suspended by an examiner’s hands in the child’s axilla. The child would slip through the examiner’s hands if lateral pressure were not applied. “Transiently impaired” describe children who have a primary diagnosis of idiopathic hypotonia, but after the age of at least three years had no other physical or cognitive problems. “Minimally impaired” describe children who have a primary diagnosis of idiopathic hypotonia and after the age of at least three have minimal impairments such and learning disability and language delay, but do not demonstrate any other major motor impairment. “Globally impaired” describe children who have a primary diagnosis of hypotonia in infancy and also have mental retardation or a recognizable genetic or developmental diagnosis.
Subjects in this study were chosen from a database at a regional diagnostic center for developmental disorders. To be chosen, the subjects must have displayed hypotonia in infancy, been evaluated at the center before two years of age and currently be greater than three years of age. The time frame of the database extended from 1984 to 2002. The database used indicated that the primary diagnosis was hypotonia. Five hundred and three subjects were retrieved through the database using these criteria. The average age at the time of the diagnosis was 11.2 months (SD = 6.5) with 54% being diagnosed before the age of 12 months. The children were diagnosed by a developmental pediatrician who used the physical signs of head lag, slip through, astasis, hip abduction range of motion and dorsi flexion range of motion to diagnose hypotonia. Most of the children (59%) were referred for diagnostic workup because of concerns regarding developmental delay.
A parental survey was developed to capture the outcomes of these children. The survey was developed by a developmental pediatrician based on his expertise and experience in following children with hypotonia and based on the findings from previous studies. The survey was not piloted nor validated. The Appendix contains the parental questionnaire. The parents/guardians of all 503 children were contacted via postal mail and asked to sign an authorization to allow the researchers to collect data from the child’s protected medical records, read and sign an informed consent form, and finally, to fill out a questionnaire regarding the child’s current status and participation in early intervention and subsequent services. The parents were asked to return the information in the addressed and postage paid envelope provided. The researchers then made phone contact attempts with each parent/guardian asking if they had received the questionnaire and encouraging them to participate in the research. After approximately 30 days, those that still had not responded were contacted by mail with a postcard again asking for their participation. This study was approved by the institutional Committee on the Use of Human Subjects in Research and the community wide review board for human subject research.
Response Rate and Demographics
Of the 503 in the original database, 121 parents/guardians consented to participate. Also, 34 questionnaire packets were returned with incorrect addresses and 87 individuals had disconnected phones. Considering this attrition from the original database, the overall response rate was 31.6%. The parents authorized the researchers to view the child’s medical file and returned a questionnaire. Five of these subject’s medical files at the center were unavailable, and 11 were found not to fit the age requirement upon review of the medical records. The total number of subjects analyzed was 105. Ages ranged from three to 18 years with a mean age of 8.5 years (SD = 3.76), and the median age was eight years. The numbers of children grouped by ages were as follows: three to less than five years = 23; five to less than seven years = 21; seven to less than nine years = 12; nine to less than 11 years = 23; 11 to less than 13 years = 10; 13 years and greater = 16. The gender frequency was 61 males and 44 females.
The children were categorized according to the reported diagnoses in the medical record and problems or diagnoses reported on the parental questionnaire. A transient group (11 children or 10.5%) had no other diagnosis from the time of the initial diagnosis of hypotonia. A minimally impaired group (34 children or 32.4%) had mild problems such as learning disability, language delay, or attention deficit hyperactivity disorder (ADHD) but no other major motor related diagnosis except for hypotonia as an infant. A globally impaired group (43 children or 40.9%) had mental retardation or a recognizable genetic or developmental diagnosis. A fourth group consisted of children with other diagnoses, including cerebral palsy (17 children or 16.2%). The researchers decided not to include this fourth group in the global impairment group because the variety impairments were thought to be too confounding. The children in the “global” or “other” were initially diagnosed with hypotonia in infancy, but following further diagnostic work, underlying problems were found. Further analysis of the outcome data provided by the parents compared just three categories of children, the two idiopathic groups (transient group and the minimally impaired group) and the globally impaired group. Table 1 displays the frequency of the reported diagnoses and problems among two categories of children. The transient group is excluded because by definition they did not have any residual problems. Learning disability and language delay were frequent sited problems among the minimal impairment group.
The frequency of various outcomes and difficulties among the three groups as reported in the parental questionnaire is displayed in Table 2. Because age may be a factor in these outcomes, the frequencies are also given for those above and below age eight years. A statistical difference existed between the frequency of the children in the two age groups for the reported problems of custom shoe inserts (χ23 = 6.7, p = 0.01) and feeding difficulties (χ23 = 4.63, p = 0.03). Only subjects age eight years and above were included in the frequency analysis of poor handwriting, and difficulty in math and reading. Table 2 includes only those reported problems in which at least 10% of the children within the three diagnostic categories had a reported problem. Poor coordination was cited for more than 50% of the children in the minimal impairment group with no difference between the age groups. More than 30% of the parents in the minimal impairment group indicated that their children’s walking was clumsy, and their children were distractible and inattentive. In the eight years or older minimal impairment group the frequency of children who were reported as distractible and inattentive was over 50%. Figure 1 displays the relative difference in frequency for outcomes among the three groups.
Frequency statistics regarding the use of various resources among the three groups as reported in the parental questionnaire are found on Table 3. Speech therapy, occupational therapy, and physical therapy were all highly utilized in the minimal impairment group. A moderately high utilization beyond two years was also reported. The frequency of family history of disability/deficit is reported in Table 4. Overall frequency of family history of deficit was low, but global and minimal impairment groups displayed overall higher frequencies individually than the transient group.
Independent sample t tests were performed to determine whether a significant difference existed between the minimal impairment and global impairment groups in regards to the developmental quotients (DQs) at initial evaluation and age at walking (see Table 5). The development quotient was calculated by dividing the developmental age, as determined by a standardized test, by the actual age in months, then multiplying by 100. A DQ of 100 represents the mean of normally developing children with a standard deviation of 15. Children scoring above one standard deviation (>85) are considered to be developing normally. Upon the review of the medical records, not all the children were administered a standardized test to determine a developmental quotient. Thus the data reflect a sub sample of the original group. A statistically significant difference was found between the means of all the DQs except for the initial gross motor and initial expressive language DQs. The heterogeneity of the group size precluded an analysis of variance of the three groups. Some of the records included the test and raw scores, and some just reported the DQ and did not specify the test. The reported standardized tests used to determine the DQs for gross and fine motor included the Peabody Developmental Motor Scale (86% of the subjects) and the Batelle Developmental Index (13% of the subjects). For cognitive skills, the Cognitive Adaptive Test/Clinical Linguistic and Auditory Millstones Scale (CAT/CLAMS) was used for 62% of the subjects. For language skills the CAT/CLAMS (45% of the subjects) and Rosetti Infant Language Scale (45% of the subjects) were used.
Early Developmental Differences
In this group of children, the mean DQs were less than the standard score of 100. The mean of each group indicated delayed developmental quotients (DQs <70) for gross motor skills at the initial evaluation. The minimal impairment group had initial fine motor, cognitive and receptive language skills DQs above the level of delayed (>70) and statistically higher than the global impairment group. These results suggest that developmental quotients determined at initial evaluations, especially fine motor, cognitive and receptive language skills may be helpful in determining outcomes of children that present with hypotonia as infants. These results should be taken cautiously since not all the subjects underwent developmental testing. Further research on the relationship between initial DQs and outcomes on a larger sample size would be beneficial, as would research correlating specific ranges of DQs with certain outcomes.
The reported age when walking well was observed in both the minimal and globally impaired group was to be about 22 months and 30 months, respectively. Walton had similar findings, as he reported a delay in the attainment of motor milestones in the BCH population.2 This result should be taken only generally since it was derived from the survey question “At what age did your child walk well on his own?” The question did not specify any criteria for “walking well on own” and thus may have been open to some interpretation.
The manifestations of impaired motor functioning were also detected in this study. Almost 59% of the minimal impairment group was reported to have poor coordination and 35% were reported to display clumsy walking. These results varied slightly from the study done by Shuper et al., who found half of a similar group of subjects to have clumsy gait.11 In the older minimal impairment group, 58% were reported as having poor handwriting, 70% had difficulties in math, 58% were inattentive, and 53% were distractible. All of these outcomes occurred more frequently in the minimal impairment group as compared to the transient group. Some in the minimal impairment group were diagnosed with a learning disability (44%). However, a greater frequency of parents was concerned about specific related learning issues, perhaps indicating under diagnosis of learning disability in the group with idiopathic hypotonia. These results are also consistent with what therapists have indicated as characteristics of hypotonia.13
Speech therapy, physical therapy, and occupational therapy were highly used in the minimal impairment group, with almost 83% of the transient and minimal impairment subjects receiving physical therapy and approximately 91% receiving speech therapy. The utilization of speech therapy beyond two years was still high (90.7%). This statistic supports the results of Shuper, who found half of the subjects with BCH to display speech delay.11 In this study, data were not collected to clearly determine the exact age at which these services were begun, but research in this area is recommended to determine if there is a delay in the commencement of needed services in the minimally impaired population of patients born with idiopathic hypotonia as compared to when services are begun in the more globally impaired diagnoses.
The last area we addressed was familial incidence of idiopathic hypotonia. Parush found in his report a high familial incidence of BCH.3 In this study, we noted that the presence of learning disability, ADHD, motor deficit, and neurological deficit in the family history, were each more frequently found in the minimal and transient groups combined as compared to the global group, though the overall frequency was small.
A limitation of this study was the relatively low response rate and overall number of subjects. Though 10.5% of the infants diagnosed with hypotonia had little to no residual problems (the transient group) and 32.4% had minimal impairments, it is difficult to say if this percentage is reflective of the population of children that are diagnosed with hypotonia. Also with this response rate it is difficult to say if those parents that did respond are representative of the population. Parents more affected by the hypotonia of their child may have been more inclined to respond. Despite these limitations, the relative percentages of the outcomes within a group were similar to what the previous researchers have found. Another limitation of the study was the questionnaire used was not validated. Because wide variations occur in even normal development, the data should be considered only as a general and potential trend in this group of children.
The overall aim of this study was to better understand the outcomes related to infant-diagnosed idiopathic hypotonia. We found that children diagnosed with idiopathic hypotonia in infancy typically had developmental scores below the standard score of 100 but were considered delayed initially (DQ <70) in only gross motor and expressive language skills. All the developmental scores were lower in those with global impairments. With regard to outcomes later in life, these children walked later than normal; heavily utilized rehabilitation services; and often demonstrated learning, language and motor deficits later in life.
The findings in this study may inform pediatric therapists of the expected outcomes for children with hypotonia and may assist therapists in developing further outcome and interventional research in this area. These findings may also assist parents, teachers, therapists and other resource providers to better anticipate a child’s needs and allow for more informed decisions when considering the need for services.
Further research is warranted to look more closely at the specifics regarding resources utilized by this group such as age at initiation of services, span of services, and frequency of services. More research is also needed in the area of idiopathic hypotonia and learning disability later in life, as well as familial incidence of idiopathic hypotonia. Further research is also warranted on the relationship of developmental quotients to serve as tools in determining a functional prognosis for these children. A larger sample size is recommended for future studies. The findings of this study should be taken cautiously. This was a retrospective study based on incomplete medical records. These findings need to be confirmed by a prospective study from the time of initial diagnosis to later years using established measurement instruments and follow-up methodology.
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New York, NY: the Guilford Press; 1999:385–405.
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The following is a questionnaire that asks questions about your child, his or her current function, what services they may have received. Please answer the questions to the best of your ability. The questionnaire should only take 5–10 minutes. If you have questions about any of the items, please call XXXX at XXXX. Your participation is appreciated and your contribution will greatly assist us in understanding hypotonia.
1. The current age of your child:____years _____ months
2. What grade is your child in:_____________
3. Is he or she in full-time special education:___Yes ___No
4. Is he or she receiving resources services: ___Yes ___No
5. Does he or she have an IEP (Individualized Education Plan): ___Yes ___No
6. Has your child had any of the following services, and if so, for how long:
Physical Therapy: If Yes, for how long
__Yes __No ___Less than 1 year
___Greater than 2 years
Occupational Therapy: If Yes, for how long
__Yes __ No ___Less than 1 year
___Greater than 2 years
Speech Therapy: If Yes, for how long
__Yes __No ___Less than 1 year
___Greater than 2 years
Other Services: (please explain)
For how long were other services were received:Less than 1 year
Greater than 2 years
7. Has your child ever been diagnosed with a learning disability? ___Yes ___No
8. Please indicate with a check mark if your child has ever been diagnosed with:
___ Autism spectrum disorder including Aspergers Syndrome
___ Motor Apraxia
___ Sensory Integration Disorder
___ Language delay
___ Verbal Apraxia
___ Mental Retardation
___ Cerebral Palsy
___ Behavior Disorder
___ Other diagnosis – Please explain
9. At what age did your child walk well on his own: _____ months old
10. Please indicate with a check mark any of the following that describe your child currently:
___Walks independently with good coordination
___Walks independently but is clumsy
___Uses a walker, cane or crutches to walk
___Uses a wheelchair
___Uses a stroller
___Rolls/crawls to get around
___Wears custom shoe inserts
___Wears ankle/foot braces
11. Please indicate with a check mark any of the following that describe your child currently:
___Clumsy or poor motor coordination
___Difficulty with reading
___Difficulty with math
This concludes the survey – please follow the directions below.
Please place this questionnaire and the consent form you signed in the addressed postage paid envelope provided. Then drop in the mail at your earliest convenience.
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