The effects of cranial irradiation on growth hormone secretion

The impact of childhood cancer and its treatment on puberty and subsequent hypothalamic pituitary and gonadal function, in both boys and girls

Childhood cancer survivors (CCS) are at an increased risk of endocrine disorders. Disorders of the hypothalamic-pituitary-gonadal (HPG) axis are a particular concern because of their impact on pubertal development and future fertility and may be of central (hypothalamic or pituitary damage) or primary (gonadal) origin. Hypogonadism may present as pubertal disorders during adolescence and subsequent infertility in adulthood but should be anticipated to ensure appropriate surveillance is in place to address these issues at an appropriate age. Those at risk of HPG axis dysfunction include those with tumours primarily affecting the hypothalamus, pituitary or gonads themselves or due to their treatment with surgery, radiotherapy and chemotherapy. CCS who have had cranial irradiation of more than 30 Gy are at risk of gonadotrophin deficiency. Those who have had gonadotoxic chemotherapy, especially alkylating agents or radiotherapy to the gonads are at risk of primary gonadal failure. HSCT survivors who have had chemotherapy and total body irradiation are at risk of primary gonadal failure but may also have gonadotrophin deficiency. Understanding those at risk is essential to appropriate counselling and long-term follow-up. This chapter gives an overview on the impact of childhood cancer and its treatment on puberty, gonadal function and fertility in childhood cancer survivors.

60 YEARS OF NEUROENDOCRINOLOGY: The hypothalamo-GH axis: the past 60 years

At the time of the publication of Geoffrey Harris's monograph on 'Neural control of the pituitary gland' 60 years ago, the pituitary was recognised to produce a growth factor, and extracts administered to children with hypopituitarism could accelerate growth. Since then our understanding of the neuroendocrinology of the GH axis has included identification of the key central components of the GH axis: GH-releasing hormone and somatostatin (SST) in the 1970s and 1980s and ghrelin in the 1990s. Characterisation of the physiological control of the axis was significantly advanced by frequent blood sampling studies in the 1980s and 1990s; the pulsatile pattern of GH secretion and the factors that influenced the frequency and amplitude of the pulses have been defined. Over the same time, spontaneously occurring and targeted mutations in the GH axis in rodents combined with the recognition of genetic causes of familial hypopituitarism demonstrated the key factors controlling pituitary development. As the understanding of the control of GH secretion advanced, developments of treatments for GH axis disorders have evolved. Administration of pituitary-derived human GH was followed by the introduction of recombinant human GH in the 1980s, and, more recently, by long-acting GH preparations. For GH excess disorders, dopamine agonists were used first followed by SST analogues, and in 2005 the GH receptor blocker pegvisomant was introduced. This review will cover the evolution of these discoveries and build a picture of our current understanding of the hypothalamo-GH axis.

Effect of cancer treatment on hypothalamic-pituitary function

The past 30 years have seen a great improvement in survival of children and young adults treated for cancer. Cancer treatment can put patients at risk of health problems that can develop many years later, most commonly affecting the endocrine system. Patients treated with cranial radiotherapy often develop dysfunction of the hypothalamic-pituitary axis. A characteristic pattern of hormone deficiencies develops over several years. Growth hormone is disrupted most often, followed by gonadal, adrenal, and thyroid hormones, leading to abnormal growth and puberty in children, and affecting general wellbeing and fertility in adults. The severity and rate of development of hypopituitarism is determined by the dose of radiotherapy delivered to the hypothalamic-pituitary axis. Individual growth hormone deficiencies can develop after a dose as low as 10 Gy, whereas multiple hormone deficiencies are common after 60 Gy. New techniques in radiotherapy aim to reduce the effect on the hypothalamic-pituitary axis by minimising the dose received. Patients taking cytotoxic drugs do not often develop overt hypopituitarism, although the effect of radiotherapy might be enhanced. The exception is adrenal insufficiency caused by glucocorticosteroids which, although transient, can be life-threatening. New biological drugs to treat cancer can cause autoimmune hypophysitis and hypopituitarism; therefore, oncologists and endocrinologists should be vigilant and work together to optimise patient outcomes.

Alternative causes of hypopituitarism: traumatic brain injury, cranial irradiation, and infections

Hypopituitarism often remains unrecognized due to subtle clinical manifestations. Anterior pituitary hormone deficiencies may present as isolated or multiple and may be transient or permanent. Traumatic brain injury (TBI) is recognized as a risk factor for hypopituitarism, most frequently presenting with isolated growth hormone deficiency (GHD). Data analysis shows that about 15% of patients with TBI have some degree of hypopituitarism which if not recognized may be mistakenly ascribed to persistent neurologic injury and cognitive impairment. Identification of predictors for hypopituitarism after TBI is important, one of them being the severity of TBI. The mechanisms involve lesions in the hypothalamic-pituitary axis and inflammatory changes in the central nervous system (CNS). With time, hypopituitarism after TBI may progress or reverse. Cranial irradiation is another important risk factor for hypopituitarism. Deficiencies in anterior pituitary hormone secretion (partial or complete) occur following radiation damage to the hypothalamic-pituitary region, the severity and frequency of which correlate with the total radiation dose delivered to the region and the length of follow-up. These radiation-induced hormone deficiencies are irreversible and progressive. Despite numerous case reports, the incidence of hypothalamic-pituitary dysfunction following infectious diseases of the CNS has been underestimated. Hypopituitarism usually relates to the severity of the disease, type of causative agent (bacterial, TBC, fungal, or viral) and primary localization of the infection. Unrecognized hypopituitarism may be misdiagnosed as postencephalitic syndrome, while the presence of a sellar mass with suprasellar extension may be misdiagnosed as pituitary macroadenoma in a patient with pituitary abscess which is potentially a life-threatening disease.

Hypopituitarism following radiotherapy

Deficiencies in anterior pituitary hormones secretion ranging from subtle to complete occur following radiation damage to the hypothalamic-pituitary (h-p) axis, the severity and frequency of which correlate with the total radiation dose delivered to the h-p axis and the length of follow up. Selective radiosensitivity of the neuroendocrine axes, with the GH axis being the most vulnerable, accounts for the high frequency of GH deficiency, which usually occurs in isolation following irradiation of the h-p axis with doses less than 30 Gy. With higher radiation doses (30-50 Gy), however, the frequency of GH insufficiency substantially increases and can be as high as 50-100%. Compensatory hyperstimulation of a partially damaged h-p axis may restore normality of spontaneous GH secretion in the context of reduced but normal stimulated responses; at its extreme, endogenous hyperstimulation may limit further stimulation by insulin-induced hypoglycaemia resulting in subnormal GH responses despite normality of spontaneous GH secretion in adults. In children, failure of the hyperstimulated partially damaged h-p axis to meet the increased demands for GH during growth and puberty may explain what has previously been described as radiation-induced GH neurosecretory dysfunction and, unlike in adults, the ITT remains the gold standard for assessing h-p functional reserve. Thyroid-stimulating hormone (TSH) and ACTH deficiency occur after intensive irradiation only (>50 Gy) with a long-term cumulative frequency of 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose less than 30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia, due to hypothalamic damage leading to reduced dopamine release, has been described in both sexes and all ages but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies (30-60% after 10 years) occur after more intensive irradiation (>60 Gy) used for nasopharyngeal carcinomas and tumors of the skull base, and following conventional irradiation (30-50 Gy) for pituitary tumors. The frequency of hypopituitarism following stereotactic radiotherapy for pituitary tumors is mostly seen after long-term follow up and is similar to that following conventional irradiation. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy.

Growth and growth hormone therapy of children treated for leukaemia

A total of 37 children (24 male, 13 female) who had been treated for leukaemia with chemotherapy and 24 Gy cranial irradiation, and who were disease free for at least 18 months, were commenced on somatrem at a mean of 7.6 years (range, 4.8-12.1 years) after leukaemia diagnosis because of growth rate below the 25th centile for bone age. Peak GH response to provocation (exercise, arginine, insulin hypoglycaemia) was less than 20 milliunits/litre in 27 children (deficient group) and 20 milliunits/litre or more in 10 children (non-deficient group). The mean height SD decrease from diagnosis of leukaemia to commencement of somatrem was 1.98, 86% of the children decreasing by more than 1 SD. Those who were tall for age at leukaemia diagnosis and females were more severely affected. Mean (+/- SD) height velocity increased on somatrem from 2.7 +/- 1.1 to 6.6 +/- 2.2 cm/year during the first 6 months (n = 25), and to 6.0 +/- 1.7 cm/year during the first 12 months (n = 19). No difference in growth response was seen between the sexes or between the deficient and non-deficient groups. Catch-up growth occurred for the first 6 months only. It is concluded that children with a low growth rate after treatment of leukaemia should be considered for GH therapy irrespective of the results of GH provocative tests.

Cranial irradiation and growth hormone neurosecretory dysfunction: a critical appraisal

CONTEXT

It has been suggested that radiation-induced GH neurosecretory dysfunction exists in children; however, the pathophysiology is poorly understood, and it is unknown if such a phenomenon exists in adult life.

STUDY SUBJECTS

Twenty-four-hour spontaneous GH secretion was studied by 20-min sampling both in the fed state (n = 16; six women) and the last 24 h of 33-h fast (n = 10; three women) in adult cancer survivors of normal GH status defined by two GH provocative tests, 13.1 +/- 1.6 (range, 3-28) yr after cranial irradiation (18-40 Gy) for nonpituitary brain tumors (n = 12) or leukemia (n = 4) in comparison with 30 (nine women) age- and body mass index-matched normal controls (fasting, 11 men and three women).

RESULTS

Using previously published diagnostic thresholds, all patients had stimulated peak GH responses in the normal range to both the insulin tolerance test and the combined GHRH plus arginine stimulation test, as well as normal individual mean profile GH levels during the fed and fasting states. However, gender-specific comparisons revealed marked reduction (by 40%) in the overall peak GH responses to both provocative tests but similar GH secretory profiles; no differences were seen in the pulsatile attributes of GH secretion (cluster analysis) or the profile absolute and mean GH levels in the fed state or when the hypothalamic-pituitary axis was stimulated by fasting.

CONCLUSIONS

Radiation-induced GH neurosecretory dysfunction either does not exist or is a very rare phenomenon in irradiated adult cancer survivors. The normality of physiological GH secretion in the context of reduced maximum somatotroph reserve suggests compensatory overdrive of the partially damaged somatotroph axis and constitutes a relative argument against somatotroph dysfunction being explained purely by hypothalamic damage with secondary atrophy due to GHRH deficiency. It is therefore possible that radiation in doses less than 40 Gy causes dual damage to both the pituitary and the hypothalamus.

Late effects of treatment on growth in childhood non-Hodgkin's lymphoma

Growth impairment is one of the most important late sequelae in childhood malignancies. In the last few years, the contribution of cytotoxic agents to growth retardation has been a subject of investigation. The aim of this study was to evaluate the growth impairment in children treated for non-Hodgkin's lymphoma (NHL). The study group comprised 41 children (eight girls, 33 boys) treated for NHL with three different chemotherapy protocols. All patients were in remission at the last visit. The control group consisted of 41 healthy age- and sex-matched children. All patients' standing heights and body weights were measured regularly from the time of diagnosis. Growth parameters were measured both at the time of diagnosis and at the end of treatment (median treatment time: 6 months). Height and weight velocities were calculated at 6 month intervals after the diagnosis until the last visit. The mean height SDS of the patients was -0.66 +/- 1.42 at the diagnosis and 0.29 +/- 1.21 at the last visit. Height SDS of the patients showed a significant improvement at the end of the 2nd year after the diagnosis (p = 0.005) and at the last visit (p = 0.022) (median follow-up time: 48 months after diagnosis). The height velocity SDS increase at the end of the 2nd year was particularly remarkable in short-term protocols such as BFM-90 B-NHL. The sitting height, the sitting height/height ratio and serum insulin-like growth factor-I (IGF-I) levels were found to be lower in the patients than those of control group at the last visit. One can conclude that chemotherapy might cause a reduction in growth velocity during treatment. The cumulative dosages of anti-neoplastic agents and serum IGF-I levels could have been implied in the pathogenesis of growth retardation.

Hypopituitarism as a consequence of brain tumours and radiotherapy

Radiation-induced damage to the hypothalamic-pituitary (h-p) axis is associated with a wide spectrum of subtle and frank abnormalities in anterior pituitary hormones secretion. The frequency, rapidity of onset and the severity of these abnormalities correlate with the total radiation dose delivered to the h-p axis, as well as the fraction size, younger age at irradiation, prior pituitary compromise by tumour and/or surgery and the length of follow up. Whilst, the hypothalamus is the primary site of radiation-induced damage, secondary pituitary atrophy evolves with time due to impaired secretion of hypothalamic trophic factors and/or time-dependent direct radiation-induced damage. Selective radiosensitivity in the neuroendocrine axes with the GH axis being the most vulnerable to radiation damage accounts for the high frequency of GH deficiency, which usually occurs in isolation following irradiation of the h-p axis with doses less than 30 Gy. With higher radiation doses (30-50 Gy), however, the frequency of GH insufficiency substantially increases and can be as high as 50-100%, and TSH and ACTH deficiency start to occur with a long-term cumulative frequency of 3-6%. Abnormalities in gonadotrophin secretion are dose-dependent; precocious puberty can occur after radiation dose less than 30 Gy in girls only, and in both sexes equally with a radiation dose of 30-50 Gy. Gonadotrophin deficiency occurs infrequently and is usually a long-term complication following a minimum radiation dose of 30 Gy. Hyperprolactinemia, due to hypothalamic damage leading to reduced dopamine release, has been described in both sexes and all ages but is mostly seen in young women after intensive irradiation and is usually subclinical. A much higher incidence of gonadotrophin, ACTH and TSH deficiencies (30-60% after 10 years) occur after more intensive irradiation (>70 Gy) used for nasopharyngeal carcinomas and tumours of the skull base and following conventional irradiation (30-50 Gy) for pituitary tumours. Radiation-induced anterior pituitary hormone deficiencies are irreversible and progressive. Regular testing is mandatory to ensure timely diagnosis and early hormone replacement therapy to improve linear growth and prevent short stature in children cured from cancer, and in adults preserve sexual function, prevent ill health and osteoporosis and improve the quality of life.

Sleep in children with neoplasms of the central nervous system: case review of 14 children

OBJECTIVE

Sleep is a complex neurologic process that is generated by and primarily benefits the brain. Sleep can be disrupted by a wide range of brain injuries, many of which may occur in children with neoplasms of the central nervous system (CNS). The specific sleep problems that have been associated with brain injuries include sleepiness, apnea, insomnia, and loss of circadian rhythmicity. The objective of this study was to characterize the sleep problems seen in children with neoplasms of the CNS through a comprehensive clinical and objective sleep evaluation.

METHODS

A retrospective case series review was conducted of all children with neoplasms of the CNS referred to the sleep clinic for a clinical evaluation between 1994 and 2002. The sleep evaluation of the 14 children in this report included a sleep history, a sleep log, and a polysomnogram. In the 12 children with complaints of daytime sleepiness and/or fatigue, a multiple sleep latency test was performed the day after the polysomnogram. Three children also had a 2-week actigraphic study.

RESULTS

The most common sleep complaint in this group of children was excessive daytime sleepiness (EDS), present in 9 of the 14 children. In these children, the sleepiness was manifest by 1 or more of the following symptoms: 1) an increase in total sleep time per 24 hours; 2) the resumption of daytime naps that had been previously discontinued at a younger age; 3) an inability to awaken in the morning to begin the days activities; or 4) the inability to remain awake during activities of daily living, such as school. Of the 9 children with daytime sleepiness, 8 had brain tumors requiring neurosurgical procedures at the time of their diagnosis, 6 of whom required ventricular shunting. The children with the most severe sleepiness had evidence of hypothalamic/pituitary injury with deficiencies in both anterior and posterior pituitary hormones. Five of the children with EDS had polysomnographic evidence of symptomatic narcolepsy with rapid eye movement sleep present on 2 or more of the daytime naps. The symptoms of EDS were effectively controlled with modest doses of daytime stimulant medication and/or scheduled naps. Central apnea leading to respiratory insufficiency and requiring mechanical ventilation to correct was present in 2 children with tumors involving the medulla. Although snoring with possible obstructive sleep apnea was the reason for referral to the sleep clinic in 5 children, none of the children in this series had polysomnographic evidence of significant obstructive sleep apnea. The other sleep problems seen in these children were hypoxia in 2 children, fatigue in 3 children, and seizures during sleep in 1 child. The interval between tumor diagnosis and sleep evaluation varied from 0 months to 9 years (mean: 42 months). The treatment of the sleep problems of this group of children took many forms, including stimulants, scheduled naps, mechanical ventilation, supplemental oxygen, and anticonvulsants.

CONCLUSIONS

Brain injuries, which invariably are present in children with neoplasms of the CNS, may result in a variety of diagnosable and treatable sleep disorders. The sleep symptoms did not appear to be directly related to the specific therapy the child received, nor the presence of residual tumor. Rather, the primary determinant of the sleep symptoms was the area of the brain that was damaged, regardless of how the damage occurred. Children who sustained damage to the hypothalamic/pituitary region developed EDS regardless of whether the damage was the result of the tumor, surgery, hydrocephalus, or radiation to the whole brain or localized to the suprasellar area. The only children who developed respiratory insufficiency had an injury to the medulla. This observation is consistent with the view that sleep is a specific, albeit complex, neurologic process that is controlled by specific brain regions. EDS and respiratory insufficiency were the most commonly diagnosed severe sleep disorders in these children. The sleep problems of children with brain tumors may develop before, but more often soon after, their tumor diagnosis and treatment. However, the sleep symptoms may not be appreciated by medical providers until years after their onset, which may delay the beginning of effective interventions.

Childhood-onset growth hormone (GH) deficiency in adult life

Over the last decade GH replacement therapy for adults has progressed in status from research study to a mainstream clinical indication. An area ripe for further research, however, is the difference between adults who developed GHD before and after completion of growth and puberty. That differences exist, not only in aetiology, but also in phenotype and response to GH therapy is clear. However, whether these differences are intrinsic to the timing of onset of GHD, or related to secondary factors including the method of assessment or dose of GH employed is uncertain. This chapter discusses the current state of knowledge in this area and poses further questions, not only for the researcher attempting to understand the mechanisms underlying these differences, but also for the physician seeking to ameliorate the impact of GHD in patients who acquired GHD in childhood.

The impact of irradiation on growth hormone responsiveness to provocative agents is stimulus dependent: results in 161 individuals with radiation damage to the somatotropic axis

GH provocative tests remain the mainstay for the diagnosis of GH deficiency and at present the insulin tolerance test (ITT) is the gold standard. There are, however, a variety of other stimulation tests used in clinical practice. Each necessitates the use of a specific cut-off derived from normative data, but there remains a widely held view that the implications from a "failed" test are independent of the nature of the stimulus. We sought to examine whether this is the case in individuals with evidence of radiation damage to the somatotropic axis. One hundred and sixty-one nonacromegalic patients were identified who had undergone an arginine stimulation test (AST) and an ITT within a 3-month period as part of routine testing between 1975 and 1999. They were divided into those tested before (n = 81; 48 males) and those tested after (n = 80; 36 males) completion of growth and puberty. Patients were considered for inclusion in the study if they had a history of cranial irradiation and a GH response to one provocative test of less than 8 microg/L, taken as indicating that some damage to the GH axis may have occurred. The patients were compared with 2 control groups. The first comprised 35 adults (18 males) and the second consisted of 16 prepubertal children (10 males). The median peak (range) GH response to the ITT was significantly greater (P < 0.0001) than that to the AST in the adult controls: 24.9 (4.1--76.9) vs. 12.2 (0.88--35.0) microg/L, respectively. However, in the patients the GH responses were similar (P = 0.28): 2.2 (0.2--25.7) vs. 1.4 (0.2--12.8) microg/L to the ITT and AST, respectively. In contrast to the pattern seen in the adult controls, the response to an ITT in childhood controls was of similar magnitude (P = 0.5) to that to the AST: 17.5 (8.1--40.0) vs. 19.4 (7.3--53.8) microg/L, respectively. However in the patients, the GH response to the AST was greater than that to the ITT (P < 0.0001): 4.3 (0.7--17.2) vs. 3.0 (0.4--18.1) microg/L, respectively. In summary, we have shown that the impact of irradiation on GH responsiveness to provocative agents is stimulus dependent. The GH response to an AST appears to be more resistant to the effects of irradiation than that to the ITT. When investigating the impact of irradiation on GH secretory status, the GH response to an AST may be a less sensitive guide to the functional ability of the GH axis.

Dosimetry and growth hormone deficiency following cranial irradiation of childhood brain tumors

BACKGROUND

Dosimetry of the hypothalamus-pituitary (HP) region could allow prediction of the risk of growth hormone deficiency (GHD) following cranial irradiation.

PROCEDURE

Nineteen children (15 boys) with a median age of 6.3 years (range 1.7-16.5) at the time of irradiation of a brain tumor not involving the HP axis were followed for 1.2-6.3 years (median 3.4) from radiotherapy (RT). The dose to a standardized anatomical model including the HP region was calculated from dose-volume histograms of 10% to 100% in steps of 10% of the HP model based on data from a computer-based treatment planning system. If GHD was suspected from insulin-like growth factor-I, serum insulin-like growth factor binding protein-3, and/or height velocity measurements, an arginine stimulation test was performed. GHD was defined by a peak GH <15mU/liter.

RESULTS

Ten patients developed GHD 10-26 months from irradiation. Cox regression analysis identified the 90% dose-volume of the HP box as the strongest predictor of development of GHD (P = 0.03). The median dose to the 90% dose-volume of the HP region was 37.5 Gy (range 2. 3-55.3). The cumulated risk of GHD 2.5 years after radiotherapy for children receiving more than and less than 37.5 Gy to the HP region was 87% and 33%, respectively (P = 0.036).

CONCLUSIONS

Dosimetry of a defined HP volume provides the opportunity to 1) calculate the exact dose delivered to this region, 2) predict the risk of GHD and, 3) in the future revise the treatment planning and thus reduce the risk of endocrine adverse effects.

Growth and growth hormone secretion after treatment for childhood non-Hodgkin's lymphoma

The aim of this study was to evaluate the growth and growth hormone (GH) secretion, as assessed by the rate and pattern of secretion, in patients in remission from non-Hodgkin's lymphoma (NHL) who had been treated with corticosteroids and intense chemotherapy. None of the patients had received cranial irradiation. Twelve children were investigated yearly by taking 24-hour GH profiles starting 1 year from the time of diagnosis. The mean age at onset of the disease was 7.5 years. Another 12 young adults were studied in a cross-sectional manner 4.1-21.3 years (mean, 9.0 years) after diagnosis of NHL. The mean age at onset of the disease was 10.7 years. The median height velocity was significantly decreased during the 1st year following diagnosis (standard deviation scores [SDS] -0.15, P < .001), especially during the first 3 months (SDS -0.75, P < .001) when the most intense treatment was given. During the 2nd year height velocity was still somewhat reduced (SDS -0.13, P < .001). However, there was no reduction in final attained height. Spontaneous GH secretion, in terms of both secretory rate and pulsatile pattern, was evaluated by measuring integrated GH concentrations in 20-minute blood samples collected over a 24-hour period. The plasma GH concentrations were transformed into GH secretion rates by means of a deconvolution technique. Fourier time series analysis was applied to determine possible disturbances of rhythmicity of the GH secretion. The GH secretion rate and the pulsatile pattern of secretion in the NHL patients were similar to those of the reference population of pubertal matched healthy controls. There was no influence of the age at diagnosis or of the time from diagnosis of NHL on the GH secretion rate. Growth impairment in children with a malignant disease treated only with steroids and chemotherapy is therefore probably not caused by disturbed GH secretion, but rather by direct interference with bone growth of the cytotoxic drugs used. There was no significant influence on weight gain during the treatment period so an indirect effect of chemotherapy on bone growth through interference with adequate nutrition seems unlikely. However, GH secretion was not evaluated during the period of growth retardation, and therefore a transient deficiency was not excluded.

The effects of irradiation and chemotherapy on growth

The effects of cancer therapy on growth are reviewed. The effects of radiation and chemotherapy on growth hormone production and growth hormone responsiveness by peripheral tissues are examined. The effects of radiotherapy and chemotherapy on other endocrine function pertaining to growth also are discussed. An approach to surveillance of pediatric cancer survivors pertaining to growth and development is suggested.

Long-term follow-up of young children with brain tumors after irradiation

PURPOSE

Young children with brain tumors are at high risk of developing late sequelae after curative radiotherapy. A retrospective study was undertaken to determine the frequency and severity of neurological deficits, endocrine dysfunction, and intellectual disabilities.

METHODS AND MATERIAL

One hundred and fifty-six children age < or = 3 years were treated between 1952 and 1986 with radiotherapy. Of the 57 survivors, 47 had surgery, 12 chemotherapy and 24 children received cranio-spinal radiotherapy. Late radiation side effects were assessed with a clinical examination, blood tests and an interview.

RESULTS

The median follow-up was 13 years and the actuarial survival at 5 and 10 years was 49% and 44%, respectively. No, or only a mild, handicap was noted in 24 patients, while 21 had moderately severe and 16 severe disabilities. Children with supratentorial tumors had more abnormal neurological findings compared to those with infratentorial malignancies (p < 0.001). Eighty percent of children had endocrine abnormalities, which were more marked in children with parasellar tumors (p < 0.001). Twenty-one children were mentally retarded. In a multivariate analysis epilepsy emerged as the only significant variable independently associated with poor cognitive function.

CONCLUSION

Long-term morbidity was found to be disabling in 58% of the surviving children. These findings encourage the development of treatment strategies designed to reduce toxicity.

A novel variant of growth hormone (GH) insufficiency following low dose cranial irradiation

OBJECTIVE

We aimed to investigate the effect of low dose (1800 cGy) prophylactic cranial irradiation on physiological growth hormone secretion.

DESIGN

We performed an analysis of 24-hour serum GH profiles using 20-minute sampling.

PATIENTS

Forty-four children were studied, of whom 21 were long-term survivors of acute lymphoblastic leukaemia and 23 were normal children. They were further subdivided into prepubertal, pubertal and post-pubertal groups.

MEASUREMENTS

GH profiles were analysed by autocorrelation, Fourier transformation and spectral analysis of stationarized data, and peak detection using the Pulsar peak detection program. RESULTS In the normal children, there was a significant increase in the median (range) area under the curve (AUC) of the GH profile between the prepubertal and pubertal groups (62 (11-124) and 137 (142-158) IU/I/h respectively, (P less than 0.01)). There was also a change in the spectral analysis through puberty. The dominant frequencies were spread widely in the prepubertal and post-pubertal groups but sharply focused in the pubertal group. In the cranially irradiated children there was no significant increase in AUC between the prepubertal (62(13-110) IU/I/h) and pubertal groups (92 (14-163) IU/I/h). The wide range of dominant frequencies persisted in the pubertal cranially irradiated group due to the presence of additional high frequency pulses. The impression of a disturbance of the periodicity of GH secretion in the cranially irradiated pubertal group was further supported by the finding that the autocorrelation function in this group alone was not significantly different from that which would arise from random data.

CONCLUSIONS

A novel form of GH insufficiency has been observed after low dose irradiation in childhood in which an abnormality of periodicity and a quantitative reduction in GH secretion appears restricted to puberty.

Longitudinal growth in children with non-Hodgkin's lymphoma and children with acute lymphoblastic leukemia: comparison between unirradiated and irradiated patients

Longitudinal growth was studied in children treated for non-Hodgkin's lymphoma (NHL). The aim of the study was to compare these children's growth velocity with findings in a previous study we performed on age-matched children with acute lymphoblastic leukemia (ALL) who received cranial irradiation. Nine children with NHL with an onset time of treatment between 4 and 9 years of age (mean 6.5 years) were studied with annual body measurements taken from the time of the diagnosis and thereafter annually during the following 4 years. None of the children received cranial irradiation. During the first treatment year a significantly low mean height velocity was observed (-1.4 standard deviation score [SDS]) for the NHL group. The consecutive two 1 year periods showed a normalization of the mean height velocity. For the group of children with ALL, there was a more prominent negative effect on height during the first 2 years of treatment than for the NHL group in the present study. After the cessation of therapy, the children with NHL showed a reduced catch-up growth compared with the children with ALL. The explanation offered is that cranial irradiation has a heavier impact on growth than chemotherapy during the first 2 years of treatment, but an intense chemotherapy during the maintenance period could have a considerable impact in blunting growth.

Polygraphic sleep patterns and growth hormone secretion in children after cranial irradiation

The effects of radiotherapy on subsequent growth hormone (GH) secretion and sleep organization was studied by simultaneous evaluation of spontaneous sleep-related GH secretion (SSRGHS), arginine-insulin tolerance test (AITT) and polygraphic sleep recording in a follow up of 19 children who underwent surgical removal of an intracranial tumour and cranial radiotherapy 1-7 years previously. Electrophysiological patterns of sleep phases, the amount and distribution of sleep stages were normal, suggesting that the procedure utilized should not entail modifications of SSRGHS per se. Long-term after radiotherapy SSRGHS and AITT GH responses were lower than those of the medium-term group. The lack of correlation between SSRGHS and AITT GH secretion suggests that SSRGHS and AITT measure different aspects of GH secretion. The highest value of GH plasma level (peak) corresponded to slow wave sleep, mainly during the first non-rapid eye movement-rapid eye movement (NREM-REM) cycle, in practically all the patients. Although the SSRGHS synchronization with SWS of the first NREM-REM cycle was preserved, no sleep measure was correlated with the SSRGHS. The usefulness of polygraphic monitoring of sleep patterns was confirmed.

Endocrine disorders following treatment of childhood brain tumours

We have studied the long-term endocrine effects of treatment on 144 children treated for brain tumours. All received cranial irradiation, 86 also received spinal irradiation and 34 chemotherapy. Almost all patients (140 of 144) had evidence of growth hormone insufficiency. Treatment with growth hormone was effective in maintaining normal growth but could not restore a deficit incurred by delay in instituting treatment. The effect of spinal irradiation on spinal growth was not corrected by growth hormone. As spinal growth makes the major contribution to the pubertal growth spurt and limb length the major contribution to childhood growth, treatment with GH will have maximal effect on leg length if instituted before the onset of puberty. Primary thyroid dysfunction was found in 11 of 47 children (23%) treated with craniospinal irradiation but in none treated with cranial irradiation alone. The incidence rose to 69% of 29 children treated with spinal irradiation and chemotherapy and to 50% of four children treated with cranial irradiation and chemotherapy. This effect of chemotherapy has not previously been reported and was detected by us through measurement of serum TSH concentration. Primary thyroid dysfunction requires treatment with thyroxine to prevent increasing the risk of secondary thyroid tumours. Seven of 20 girls (35%) treated with spinal irradiation had primary ovarian dysfunction as determined by raised gonadotrophin levels. Chemotherapy increased this, but not significantly. Three of 15 boys (20%) treated with chemotherapy had primary testicular dysfunction. Gonadotrophin deficiency occurred in seven boys. Four of 90 children had deficiency of cortisol secretion in response to hypoglycaemia. These results confirm the requirement for long-term follow-up of children treated for brain tumours from the endocrine point of view. Anticipation of hormone deficiencies and replacement treatment can improve the quality of life of survivors.

Radiation and hypothalamic-pituitary function

In adults, hypopituitarism is a common consequence of external radiotherapy. The clinical manifestations may be subtle and develop insidiously many years after radiotherapy. Anterior pituitary deficiencies can therefore only be detected by regular testing, including dynamic tests of GH and ACTH reserve. Although the deficiencies most commonly develop in the order GH, gonadotrophins, ACTH then TSH, this sequence may not be predictable in an individual patient and comprehensive testing is therefore required. The tests should ideally be performed annually for at least 10 years after treatment or until deficiency has been detected and treated. It is not only the patients with pituitary disease who are at risk of developing hypopituitarism after radiotherapy. Any patient who receives a total dose of irradiation of 20 Gy or more to the hypothalamic-pituitary axis is at risk of hypopituitarism, although the threshold dose may be lower than this. This is particularly important in the long-term survivors of malignant disease in whom endocrine morbidity may be relatively common and in whom this can be easily treated, with consequent improvement in quality of life. Whilst patients who receive a high total dose of irradiation are at increased risk of developing multiple deficiencies, a higher fraction size also increases the risk of anterior pituitary failure. There is good evidence that the earliest damage to the hypothalamic-pituitary axis after external radiotherapy is at the level of the hypothalamus. However, patients who undergo pituitary ablation with interstitial radiotherapy or heavy particle beams are likely to sustain direct damage to the pituitary. In these patients, the sequence in which individual pituitary hormone deficiencies develop is generally the same as that observed with the hypothalamic damage after conventional external radiotherapy. The increasing use of radiotherapy as a means of treatment for malignant disease means that new groups of patients with potential for endocrine dysfunction are emerging. Whole body irradiation in the preparation for bone marrow transplant is one such treatment and although hypothalamic-pituitary damage appears to be confined to GH deficiency in children, longitudinal experience is limited to date, particularly in adults. The treatment of malignant disease in childhood is of particular importance in terms of the delayed endocrine sequelae. The hypothalamic-pituitary axis may not be the only endocrine tissue damaged by treatment in these patients and management is therefore more complicated. In the growing child, the potential association of growth hormone deficiency, gonadal failure or premature puberty and thyroid dysfunction mean that expert endocrine supervision is essential for optimum long-term outcome.

Normal or early development of puberty despite gonadal damage in children treated for acute lymphoblastic leukemia

To determine the timing of pubertal development and the frequency of gonadal dysfunction in children who survive acute lymphoblastic leukemia, we assessed pubertal status and the plasma levels of sex steroids, gonadotropin, and inhibin in 45 children (20 girls and 25 boys) who had received combination chemotherapy along with 24 Gy of irradiation to the cranium (modified LSA2L2 protocol). We also reexamined testicular biopsy specimens, obtained at the time of the cessation of chemotherapy, for the presence of germ cells. Germ-cell damage, indicated by marked elevations in the plasma level of follicle-stimulating hormone (P less than 0.001 for the comparison with normal children), was evident in both sexes and was confirmed in the boys by the absence of germ cells in the testicular biopsy specimens and by the small size of the testes for pubic-hair stage. Only 44 percent of the pubertal girls had measurable plasma inhibin levels, as compared with more than 93 percent of normal pubertal girls. Although plasma sex-steroid levels were normal, the secretion of luteinizing hormone in response to stimulation with gonadotropin-releasing hormone was elevated in the pubertal children (P less than 0.01 for the comparison with normal controls)--a finding that suggests compensation for decreased gonadal function. Despite clear evidence of gonadal damage, girls had early menarche at a mean age (+/- SD) of 11.95 +/- 0.91 years, as compared with the Australian standard of 12.98 +/- 1.11 years (P less than 0.01). Thus, in girls, puberty was early despite primary gonadal damage. Thirteen of 23 boys reached puberty at a mean age of 12.36 +/- 0.73 years. We conclude that treatment for acute lymphoblastic leukemia may lead to primary gonadal damage in both sexes, regardless of the age at treatment, but that the secondary characteristics of puberty develop at a normal age or, in girls, relatively early.

Increased risk of breast cancer after low-dose irradiation

A significant increase in the risk of breast cancer has been found for the most recent 5-year period of a long-term follow-up study of children subjected to scalp irradiation, in whom a carcinogenic effect was previously only apparent in the head and neck. This increased risk was found among women aged 5 to 9 years at exposure. The breast had been exposed to a low radiation dose of approximately 16 mGy.

Growth hormone response to growth hormone-releasing hormone (hp GHRH1-44) as an index of growth hormone secretory dysfunction after prophylactic cranial irradiation for acute lymphoblastic leukemia (24 grays)

The growth hormone response to growth hormone releasing hormone hp GHRH1-44 (2 micrograms/kg i.v.) was studied in 19 prepubertal children who had been irradiated with 24 Gy for acute lymphoblastic leukemia (ALL) or lymphosarcoma (LS) at a mean chronological age of 4 10/12 years (limits 10/12 to 9 years). They were evaluated after a mean time interval of 4 8/12 +/- 3/12 years and compared to 14 prepubertal children with constitutional short stature (CSS). The individual responses to GHRH were decreased in all but three of the irradiated children. The mean GH response was 16.7 +/- 2.5 ng/ml as compared to 52.6 +/- 8.5 ng/ml in the control group (p less than 0.001). The GH response to GHRH was not correlated with the GH response to arginine-insulin tolerance test (AITT). A decreased response to GHRH with values between 12.5 and 19.4 ng/ml was observed in four cases with normal growth rates and normal GH responses to AITT. These results suggest that an impaired GH response to GHRH is a frequent finding after cranial irradiation for ALL or LS and may be the only sign of GH secretory dysfunction. It is probably indicative of early hypothalamic impairment of GH secretion.

Irradiation-induced growth failure

Short stature may complicate the treatment during childhood of brain tumours and, to a lesser extent, ALL. A number of factors may be responsible, including spinal irradiation, malnutrition, recurrent tumour, chemotherapy, precocious puberty and radiation-induced GH deficiency. GH is always the first pituitary hormone to be affected by radiation damage to the hypothalamic-pituitary axis but larger radiation doses may result in panhypopituitarism. Some children retain normal GH responses to certain provocative stimuli, although physiological GH secretion is reduced. Nonetheless, in children suspected of radiation-induced GH deficiency, pharmacological tests of GH secretion remain useful, the ITT being the test of choice because of the marked radiation sensitivity of the GH response to hypoglycaemia. The hypothalamus is more radiosensitive than the pituitary. In many patients with radiation-induced GH deficiency, the damage appears to be at the hypothalamic level resulting in a deficiency of endogenous GRF. Treatment with synthetic GRF may provide an alternative to GH therapy in such children. Finally, there is no evidence to suggest that GH therapy given to a child with radiation-induced GH deficiency might induce a brain tumour recurrence or a relapse of ALL.