Continuing Education Activity

Dwarfism is the medical terminology for short-stature. It is defined as height-vertex below two standard deviations (-2SD) or in the third percentile for a given age and sex. The standing height is measured from ground to the vertex when the head is in the Frankfurt-horizontal plane. This activity outlines the evaluation and management of dwarfism and highlights the interprofessional team's role in managing patients with this condition.

Objectives:

• Identify the etiology of dwarfism.
• Outline the evaluation of dwarfism.
• Review the management options available for dwarfism.

Introduction

Dwarfism is the medical terminology for short-stature. It is defined as height-vertex below two standard deviations (-2SD) or in the third percentile for a given age and sex. The standing height is measured from ground to the vertex when the head is in the Frankfurt-horizontal plane. Most people have an aversion to the term dwarf and identify themselves as "Little people" and also have a community under the name -'Little People of America'.

Dwarfism is broadly categorized into two types based on the patient's physical appearance, which are: proportionate short stature (PSS) and disproportionate short stature (DSS). Proportionate short stature (PSS), as the name suggests, means that the limbs and the trunk are proportionately small. Whereas, disproportionate short stature (DSS) implies that the individual has a significant difference in their sitting and standing height, and either their trunk or extremities are small. The child's assessment and evaluation aim to identify the pathological causes of short stature and intervene accordingly.

Etiology

The short stature can either be due to an underlying medical condition or a standard variant of growth. FSS, CDGP, and ISS described below can be considered as normal variants of growth, while the rest are pathological causes-

1. Familial Short Stature (FSS): The child's genetic height potential can be measured by measuring the mid-parental height, which is a child's projected adult height based on parental height measurements. A positive family history, and the absence of underlying pathological etiologies of dwarfism, can be diagnosed as a case of familial short stature. This child has an expected growth velocity, and his bone age is consistent with the chronological age. X-Ray of the hand and wrist can establish the bone age and is a frequently used modality.

2. Constitutional delay of growth and puberty (CDGP): The child presents with short height in childhood, but attain their target height until adulthood, also known as a 'late bloomer'. They even enter puberty at later ages. Unlike in familial cases, these children have bone age lagging behind the chronological age. Malnutrition in gestational age or childhood, even genetics, could be the plausible cause for this short stature pattern.

3. Idiopathic Short Stature (ISS): Short stature is said to be idiopathic when no other etiology like endocrine/metabolic can be determined. With the advancements in genomic studies, it is found that many cases previously established as idiopathic can be explained by hundreds of genetic mutations with small or large effects. The role of epigenetics is also in discussion.[1][2]

4. Endocrine disorders: Growth hormone deficiency is a frequent cause of dwarfism. The hypothalamic-pituitary axis maintains the levels of growth hormones in the body, which then directly or indirectly, through Insulin-like growth factor-1 (IGF-1), stimulates bone elongation, and growth of soft tissue and cartilage. Lower levels of IGF-1 are linked with short stature. Precocious puberty is defined as the attainment of puberty before the age of 8 years in girls and nine years in boys due to the premature release of gonadotropins centrally or peripherally. These gonadotropins lead to an initial growth spurt but also lead to the early maturation of the child's skeletal system resulting in short adult height.[3]

5. Genetic disorders: Many genetic conditions that are associated with short stature are- Down's, Turner's, Noonan's, 3-M, Prader-Willi, Russell-Silver, Aarskog, and short stature homeobox gene deficiency syndrome. Short stature is one clinical manifestation among several others.

6. Bone diseases: The faulty formation of bone can also lead to short stature. The bone disorders linked to dwarfism are-

Achondroplasia: It is an autosomal dominant genetic condition due to the mutation in the Fibroblast growth factor receptor-3 ( FGFR-3) gene. This gene typically limits the conversion of cartilage to bone, particularly in the long bones. In achondroplasia, this gene becomes overactive and bone formation is severely impacted in the extremities. Another cause of short-limb dwarfism is diastrophic dysplasia.[4]

Spondyloepiphyseal dysplasia: It is a cause of short-trunk dwarfism with the vertebrae's primary involvement and the proximal epiphyseal centers. Type-2 collagen matrix is abnormal, but it remains unclear how this abnormality spares the distal epiphysis, given that collagen is ubiquitous.

7. Systemic disorders: Other systemic diseases which have a secondary effect on growth are undernutrition, juvenile idiopathic arthritis, inflammatory bowel disease (IBD), celiac disease, chronic kidney disease (CKD), pulmonary/cardiac/immunologic/metabolic diseases, cancers, and glucocorticoid therapy.[5][6][7] Malnutrition can dampen the growth velocity and cause short stature. It can affect the baby in the gestational period, leading to underweight or small for gestational age (SGA) baby, or in childhood leading to stunted growth.[8]

Epidemiology

In the United States, 2.5 percent of the population is short. The Utah Study, a population-based survey of growth in children, concluded that endocrine disorders constitute only a small number of cases with short stature. People of both sexes are affected, but males are more likely to be brought to medical attention because of the prevalence of social expectations.[9]

Different ethnic groups have different average statures, which are essential to take into consideration while comparing mean parameters. Because these variations exist, it is recommended to compare the height of an individual with people from the same population only, if specific growth charts are available . Malnutrition is a notable etiology of retarded growth in kids, especially in developing countries. Many efforts have been in process by the government and non-profit organizations to curb this.[10]

Pathophysiology

The linear growth of an individual depends on the equilibrium between proliferation and senescence of cartilage cells at the growth plate. Multiple mechanisms regulate this process-

• Endocrine pathways – The hormones which promote chondrogenesis are GH, IGF-1, androgens, T3/T4 (thyroid hormones), while glucocorticoids inhibit chondrogenesis. Estrogen stimulates the release of GH and IGF-1 but also promotes chondrocyte senescence and epiphyseal fusion, and suspension of linear growth. Therefore, precocious puberty is associated with an initial growth spurt but an ultimate short adult height.[11][12]
• Proinflammatory cytokines – The chronic inflammatory conditions have elevated proinflammatory cytokines, which negatively impact the linear growth. As inflammation ceases, the cytokine levels drop, and the patient can catch up on growth.[13]
• Paracrine mechanisms – GH-IGF-1 axis is only one of the many regulatory pathways of height gain. Many autocrine and paracrine pathways are under research; mutation of these can lead to short stature or tall stature. These include many intracellular and extracellular matrix proteins like fibroblast growth factors (FGF), bone morphogenetic proteins (BMP), parathyroid hormone-related protein (PTH-RP), collagens, and proteoglycans in the cartilage extracellular matrix.
•  Intracellular pathways – SHOX gene codes for transcription factors that regulate the activity of other genes and its mutation is associated with a spectrum of clinical manifestations with Leri-Weill dyschondrosteosis (LWD) on the critical end, and nonspecific short stature on the other. LWD is a classical triad of short stature, mesomelia, and Madelung deformity.[14] Different signaling pathways that can be affected are SOX genes, MAPK pathways.

History and Physical

A thorough clinical history is vital in establishing the cause of dwarfism. The child's clinical record should include relevant data from gestation to birth, developmental milestones, and puberty emergence. A pedigree chart can be formulated to mention the family history of short stature. A psychological assessment of the patient is crucial as this disorder is associated with social stigmatization and extensive mental pressure. Anthropometric measurements are a part of regular child visits. These measurements include body weight, height vertex, truncal height, and limb length, plotted on a growth chart to compare with the mean parameters for that age, sex, and population.

Evaluation

The child under evaluation undergoes a series of biochemical and radiological tests:

Biochemical Tests

• Complete blood count for hematological diseases like anemia.
• Sweat chloride test for cystic fibrosis. Patients usually have a history of meconium ileus and pulmonary symptoms.
• Serum thyrotropin (TSH) levels and free thyroxine levels (T4) to test for hypothyroidism.
• Wintrobe sedimentation rate for inflammatory bowel disease (IBD)
• Antibody testing for celiac sprue includes anti-endomysial immunoglobulin A (IgA), immunoglobulin G (IgG), and anti-gliadin IgG titers. Antiendomysial IgA titers are more sensitive, and IgG titers are more specific.  
• Serum pre-albumin and transferrin- These values are low in undernutrition. 

Imaging 

• Anteroposterior X-ray of the left hand and wrist: It is used to predict the bone age. The radiologist uses the Greulich and Pyle or Tanner-Goldstein-Whitehouse method to calculate the bone age and forecast adult height. While the prior is a more straightforward method, the latter is more reliable.[15][16][17]

• MRI can provide evidence of any intracranial masses (craniopharyngiomas)or developmental anomalies of the pituitary. Before the GH therapy is initiated, an MRI scan should be ordered to rule out any organic lesions.

• Karyotyping: It can detect genetic disorders like Down syndrome, Turner syndrome, and others. 

  Provocative tests:  These tests are used to measure the GH reserve, but their utility is limited. They are not reproducible and do not determine the physiological secretory pattern of GH. These include- insulin tolerance test, Levodopa-propanol HCL test, Arginine HCL test, Glucagon test. Other physiological stimuli that can be used are strenuous exercise, deep sleep, and fasting. The levels of growth hormone fluctuate throughout the day, and peaks after meals, after strenuous exercise, and in a deep sleep. This property makes it an unreliable biomarker for detecting growth hormone deficiency (GHD); however, stimulated GH values of more than 10mg/dl can essentially rule out the deficit. Therefore, more predictive markers are serum IGF-1 levels (somatomedin C) and insulin-like growth factor binding protein-3 (IGFBP-3) levels. IGFBP-3 has more specificity than IGF-1. In patients in the pubertal phase, with CNS neoplasms, and poor nutrition, these markers can be abnormally high even in the presence of GHD and are unreliable.

Treatment / Management

There are various treatment options available to these kids to achieve the best possible outcomes for them. These includes:

Hormonal Therapy

Recombinant human growth hormone therapy (rhGH) is an effective treatment for patients suffering from growth hormone deficiency. Early intervention can prevent short stature and the psychosocial stress associated with it. The clinical benefits of rhGH are controversial, so its fixed dosing is based on its weight. Newer reports propose that rhGH dosing based on the children's IGF levels may be safe and provide superior outcomes. For patients with idiopathic short stature (ISS), commencing GH therapy can enhance the growth velocity and mean adult height. Hence, it might be suitable to say that the decision to give rhGH does not only depend on the etiology of short stature, i.e., whether it is due to ISS or GHD but also on the status of the epiphyseal maturation, mid-parental height, etc.these markers can be abnormally high even in the presence of GHD and are unreliable.[18][19]

Gonadotropin-releasing hormone (GnRH) analogs are used to halt the progression of precocious puberty. When administered, these analogs continuously suppress the release of gonadotropins from the pituitary and further down the gonadal steroids, which were responsible for premature bone maturation.

Surgical Treatment

Brain tumors need neurosurgery intervention. The limb-lengthening procedures are not recommended as they have high morbidity and mortality.

Differential Diagnosis

The differential diagnoses for dwarfism include the following:

1. Endocrine disorders: Growth hormone deficiency, congenital hypothyroidism, Cushing syndrome, hypogonadism.
2. Genetic disorders: Down's, Turner's, Noonan's, 3-M, Prader-Willi, Russell-Silver, Aarskog, and short stature homeobox gene deficiency syndrome.
3. Bone disorders: Achondroplasia, Diastrophic dysplasia, Spndyloepiphyseal dysplasia.
4. Chronic conditions: Chronic renal insufficiency, chronic malnutrition, cystic fibrosis, juvenile idiopathic arthritis, inflammatory bowel disease, celiac disease, pulmonary/cardiac/immunologic/metabolic diseases, cancers, and glucocorticoid therapy.

Treatment Planning

The child receives daily subcutaneous growth hormone (GH) injections, and are advised to take GH injections regularly, preferably within 1 hour of sleep every night, at a specific time, and not to miss more than one dose a month. The patient usually follows-up 2 to 4 times a year. The growth rate is maximum in the first year of treatment, ranging from 8-10cm/year; this is called 'catch-up growth.' The growth rate slows in the next several years, called the 'waning effect.' If the growth rate is slower than expected, it warrants further investigation to rule out other medical conditions like Hypothyroidism or IBD. The treatment continues until the patient reaches her full adult height or reaches full bone maturity or has grown less than 2 cm in the last year.

Prognosis

The normal variants of short stature can expect to lead healthy lives. The patients suffering from GHD can benefit from recombinant human growth hormone therapy and generally attain heights similar to their parents, given that the treatment is commenced before puberty. The short stature secondary to genetic and skeletal disorders cannot be reversed and remains a life long issue.

Complications

Short stature may be an indicator of chronic occult disease and need a thorough workup. These children have a lower bone density than the taller population, but its association with osteoporosis is unclear. Other common complications associated with disproportionate dwarfism are bowed legs, arthritis, kyphosis, spinal stenosis, syringomyelia, sleep apnea, hydrocephalus, weight gain.

The complications which are associated with GH therapy are- possible predisposition to type-2 diabetes, benign intracranial hypertension, edema/carpal tunnel syndrome, slipped capital femoral epiphysis (SCFE), scoliosis, prepubertal gynecomastia. Management of these complications can be done by temporary therapy termination until resolving symptoms and restarting later at lower doses.

Consultations

The following consultations are required:

• Pediatric cardiologist, radiologist, and audiologist for patients with Turner syndrome.

• Consult a psychologist for patients with mental illnesses and those facing psychosocial stressors.[20]

• Pediatric endocrinologist for GHD workup and provocative testing.

Deterrence and Patient Education

The patients and family members should be educated about the clinical basis, aetiologies, and treatment options for short stature. For patients who are planned for growth hormone therapy should be informed about the following:

• The GH used in treatment is similar to GH released from the pituitary gland and is safe and effective.
• The patient can experience foot growth within 6-8 weeks of treatment, increase appetite, increase lean body mass, and decrease fat. 
• Routine consults with the pediatric endocrinologist, blood test, and X-ray to monitor the child's progress.
• Long term commitment to the treatment.
• Importance of compliance for best outcomes.
• The patient needs to be informed about the administration technique, injection sites, timings, and the drug's refrigerating requirements for optimum efficacy.
• The possible side effects- 
• Allergic reaction, rash, or swelling at the injection site.
• Hip, knee, or other joint pain indicative of slipped capital femoral epiphysis.
• Headache may be indicative of benign intracranial hypertension.
• Progression of scoliosis.
• Temporary increase in blood sugar levels. Management of these complications can be done by temporary therapy termination until resolving symptoms and restarting later at lower doses.

Enhancing Healthcare Team Outcomes

The physicians working in children's healthcare need alertness to detect errant growth rates and provide patient-centered interventions. These kids require long term monitoring, documentation in the growth charts, and physicians' judgment of employing growth hormone therapy. Regular counseling sessions help to educate the patient and family members and improve the outcomes. The psychologist and psychiatrist may need to intervene in children facing psychosocial stressors, eating disorders, and other mental illnesses.[20]