Margaret R. Zacharin*†, Joseph Pua* and Shankar Kanumakala*
* Department of Endocrinology & Diabetes, Royal Children’s Hospital, Melbourne, Australia and †Department of Endocrinology, St Vincent’s Hospital, Melbourne, Australia.
Margaret Zacharin Department of Endocrinology & Diabetes, Royal Children’s Hospital, Parkville 3052, Australia. Tel.: +61-3-9345 5951; Fax: +61-3-9347 7763; ; E-mail: [email protected].
Summary
BACKGROUND: Osteoporosis is a common complication of untreated male hypogonadism. Even mild hypogonadism due to suboptimal testosterone replace-ment may result in decreased bone mineralization and osteoporosis.
OBJECTIVE: To assess bone mineral density in hypo- gonadal men following long-term long-acting subcuta-neous testosterone pellet implants as replacement therapy.
PATIENTS: A cross-sectional study of 37 patients with primary or secondary hypogonadism receiving longterm (mean 66 years) subcutaneous testosterone pellet implants as replacement therapy.
MEASUREMENTS: Bone mineral density was measured in all patients using dual energy X-ray absorptiometry. Serum testosterone 3-4 months after insertion of pellets was measured in all patients to assess adequacy of replacement therapy.
RESULTS: Mean areal bone mineral density were 102 (SD 014) g/cm2 with a mean Z score of -064 (SD 13) and 087 (SD 013) g/cm2 with a mean Z score of - 072 (SD 12) at lumbar spine and neck of femur, respectively. Mean serum testosterone 3-4 months after pellets insertion was 1545 nmol/l (SD 42 nmol/l). There was no significant correlation between bone mineral density and patient’s age at start or duration of testosterone therapy.
CONCLUSIONS: Bone mineral density in long-term reg-ularly treated hypogonadal men was not different from the age-matched reference range for normal men. Long- acting subcutaneous testosterone pellet implants as replacement therapy in male hypogonadism are safe, acceptable to the patient, result in adequate bone mass accumulation and maintenance of normal bone mineral density. By provision of sustained physiological levels of testosterone they may contribute to increased androgen effect at the receptor level.
Bone mass in adulthood is determined by peak bone accumulation achieved during growth and puberty and subsequent rate of bone loss (Glastre et al., 1990; Lu et al, 1992). A progressive increase in areal bone density but not volume, occurs throughout childhood, with a marked increase in bone mineralization during puberty (Rubin et al., 1993). Increases in serum androgens during puberty allow for skeletal maturation and attainment of peak bone mass, and the persistence of normal testosterone (T) secretion in adulthood is important for maintenance of bone density (Katznelson, 1998). In patients with hypogonadism due to T deficiency, decreased bone mass accumulation with heightened bone turnover lead to premature osteopaenia or osteoporosis (Medras et al., 2000; Snyder et al, 2000). In addition, patients with inadequately treated or untreated hypogonadism continue to have an increased rate of bone loss (Daniell et al., 2000).
A variety of T preparations such as oral, intramuscular, sub-lingual, trans-dermal and trans-scrotal patches have been used for replacement treatment of male hypogonadism (Arisaka et al., 1995; Leifke et al., 1998; Behre et al., 1999; Francis, 1999; Snyder et al., 2000; De Rosa et al., 2001). The choice of T preparation used, the duration of treatment and the different techniques used for measurement of bone mineral density (BMD) may explain the varying effects of T replacement therapy on BMD seen in previous studies.
There are limited published clinical data regarding the longterm use of subcutaneous T pellet implants and their efficacy in maintainance of bone mass and prevention of bone loss in hypog-onadal men. The primary objective of this study was to quantify the adult bone mass in a group of hypogonadal men, all of whom received subcutaneous pellet implants as T replacement therapy. We also aimed to assess if there was any association between BMD and clinical parameters such as patient’s age at start or duration of subcutaneous T implant treatment.
Patients and methods
All male patients with primary or secondary hypogonadism attending the Endocrine Clinic at St Vincent’s Hospital, Melbourne and who received subcutaneous T implants every 6 months were invited to participate in this study. Twenty-one patients with primary hypogonadism (12 with anorchia, seven with Klinefelter’s syndrome and two with Noonan’s syndrome) and 16 patients with secondary hypogonadism (eight with Kall- man’s syndrome and eight with hypopituitarism) participated in the study. Patient characteristics are summarized in Table 1. Only those patients who had hypopituitarism were receiving any medications other than testosterone. This group had all received complete pituitary hormone replacement and all had been treated with GH until bone age > 15-5 years. The oldest hypopituitary patient was 30 years at the time of this study and had finished GH at 18 years as it is not available for adult use in Australia. In particular, no patient had received anticonvulsant treatment, which might interfere with vitamin D metabolism. Each patient received 600-800 mg (8-10 mg/kg) of subcutaneous T pellet implants every 6 months. All patients had been diagnosed with hypogonadism either at the time of presentation with delayed puberty (Kallman’s, Klinefelter’s) or concurrently with their primary diagnosis (hypopituitarism, Noonan’s, anorchia, Klinefelter’s). Those in whom absence of puberty was anticipated were commenced on oral androgen at age 13-13-5 years. Boys presenting with pubertal delay started at an older age (15-18 years). All had received oral T (as testosterone undecanoate) and had later introduction of intramuscular T for further pubertal progress, with increasing doses over 2-3 years, until adult doses were reached. They were then changed to subcutaneous T pellet implants. The implants were inserted using a trochar and cannula, into the buttock using a previously described method (Handelsman et al, 1997; Zacharin & Warne, 1997). Serum T was analysed in all patients 3-4 months after the insertion of the implant using a chemiluminascent immunoassay for the Centaur automated analyser (Bayer Diagnostics, Victoria, Australia).
Table 1. Summary of bone mineral density measurements by patient diagnostic groups.
All participating patients had BMD measured at the time of clinic attendance. The same operator performed all BMD measurements at lumbar spine and neck of femur, using dual energy X-ray absorptiometry (DEXA), Hologic QDR 2000 densitometer (Picker Australia Pty Ltd) with 1% precision at spine and 2% precison at hip. The patient values were compared with an age- and gender-matched white population (reference ranges provided by the Hologic QDR 2000 and 4500 operators’ manual).
Statistical analyses
The BMD and Z score values between patients with hypogonadism and reference values established for normal men were compared using Student’s t-test. Significant differences between the means of different patient groups could not be determined due to the limited number of patients in each group and low statistical power for ANOVA. Regression analysis was performed to determine if there was any association between BMD and clinical parameters such as age of start and duration of subcutaneous T pellet implant therapy. Pearson’s correlation coefficient was used to determine any association between BMD and patient’s height and weight.
Results
All patients tolerated the subcutaneous T implants well without any adverse events. The mean T level measured 3-4 months after the implant insertion was 15-45 nmol/l (SD 4-2 nmol/l), which is within the normal range (9-0-35-0 nmol/l) for an adult male.
The BMD results of all patients are summarized in Table 2. The mean age of the patients at the time of measuring their BMD was 25-4 years. They had received T pellet implants for a mean 6-6 years (range 4-10 years). Mean areal BMD at lumbar spine was 1-02 g/cm2, which was an average 93-6% of normal adult reference range. Mean areal BMD at neck of femur was 0-87 g/ cm2, which was an average 91-2% of normal adult reference range. These measurements correspond to a mean Z score of -0-64 and -0-72 at lumbar spine and neck of femur, respectively. Patients’ BMD measurements at either lumbar spine (P = 0-06) or neck of femur (P = 0-24) were not statistically significant from the normal adult male reference range using a one-sample t-test.
Table 2. Summary of bone mineral density measurements by patient diagnostic groups.
Individual BMD values at lumbar spine and neck of femur for all patients are represented in Fig. 1. Individual values between patients with primary and secondary hypogonadism were not statistically different using the two-sample /-test. When analysed within each group, the mean BMD (0-86 g/cm2 and 0-75 g/cm2 at lumbar spine and neck of femur, respectively) of two patients with Noonan’s syndrome who were significantly short differed from the other patients with primary hypogonadism (P < 0-001). The BMD measurements after adjustment for height were within the normal population reference range.
Figure 1. Individual bone mineral density measurements of lumbar spine and neck of femur in all patients (g/cm2).
The regression analysis showed no significant correlation between BMD and the patient’s age at start or duration of sub-cutaneous T pellet implant therapy in our sample of long-term treated patients. However, there was an association, as expected, between the patient’s height and BMD (P = 0-01 at lumbar spine and P = 0-03 at neck of femur) and between weight and BMD (P = 0-05 at neck of femur).
Discussion
The beneficial effect of adequate T replacement therapy in hypog- onadal men is well established, in relation to changes in bone mass and biochemical markers of bone activity, independent of age and type of hypogonadism (Katznelson et al., 1996; Leifke et al., 1998; Francis, 1999; Snyder et al., 2000). This study provides evidence that regular long-term treatment with subcutaneous T pellet implants provides normal levels of serum T and results in normal bone mass accumulation.
T replacement therapy is said to be more effective during puberty and in those whose epiphyses have not fused (Eastell et al., 1998; Francis, 1999). A 5-year study of 42 patients with Klinefelter’s syndrome where 250 mg intramuscular T injections were administered to two groups, started before or after age 20, reported a significant increase in BMD in the younger age group (Kubler et al., 1992). In another study with 22 hypogonadal men, a positive correlation between BMD and duration of treatment has been reported (Canale et al., 2000). In contrast, our study demonstrated that regular and ongoing long-term adequate T replacement therapy helped all young men to attain normal BMD, regardless of age at start or duration of treatment.
A variety of dosing schedules and a variety of T preparations have been used in the past. Some investigators have reported poor outcomes in BMD following oral or intramuscular T. Twelve hypogonadal men had significantly lower spinal BMD following a mean 6-3 years treatment with 3-weekly intramuscular T enan- thate 250 mg as compared to age- and BMI-matched controls (De Rosa et al., 2001). In another study, 14 hypogonadal patients failed to reverse their low BMD after apparently adequate long-term T replacement therapy using either oral or high-dose intramuscular T for a mean 5-5 years (Wong et al, 1993). In another study, 19 of 26 hypogonadal men (73%) had their total bone min-eral content below -1 SD as compared to age-matched controls after regular treatment with intramuscular T injections (Medras et al, 2000). The pharmacokinetics of intramuscular T are far from ideal and it is necessary to give T injections every 2 weeks to provide sustained normal levels of T with this type of treatment (Sokol et al, 1982; Behre et al, 1998). Even during that time there is a 20% reduction of SHBG levels, with wide and unphysiological fluctuations in T levels (Plymate et al, 1983). The pharmacokinetics of subcutaneous T implants have been clearly described, with a sustained and constant plasma T level from 24 h after administration over a mean of 24 weeks (Handelsman et al., 1990; Behre et al., 1998) and maintenance of normal levels of SHBG. We measured normal serum T levels in all our patients 3-4 months following the pellet insertions, because a normal random T level assayed at this time implies normal integrated values for the whole 24-week period. This is also reported elsewhere (Zacharin & Warne, 1997; Kelleher et al., 2001). We suggest that sustained T levels, without marked peaks/troughs found with intramuscular injections or marked portal-peripheral gradient found with oral preparations, may contribute to the increased biological androgen effect in our sample of patients.
The BMD Z scores of -0-64 and -0-72 at lumbar spine and neck of femur, respectively, for our patients is below the mean of the population reference group. There are a number of reasons for a BMD within the young age-matched population range (Z score) but below the population mean (T score) Our patients were young adults (mean age 24-3 years), many of whom had late onset of puberty due to timing of diagnosis. T substitution is only commenced for hypopituitary patients where there is a definite lack of gonadotrophins, manifested by delay in onset of puberty. Therefore, this population had not necessarily achieved peak bone mass at the time of investigation. Delayed puberty has also been described as a cause for decreased peak bone mass (Finkelstein et al., 1992). Adequacy of previous T treatment prior to subcutaneous T implant therapy might have affected the attainment of peak bone mass, given that optimal administration intervals for intramuscular delivery of T should be 2 weeks (Sokol et al., 1982), although this schedule is seldom adhered to. However, our patients had adequate T replacement during subcutaneous T pellet implants, as shown by normal measured T concentrations at 4 months.
All standard reference ranges for BMD measurements in adults are based on age and gender but not on patient size. Thus adult patients with extreme small size or short stature can have low cross-sectional areal BMD unless adjusted for body size (Prentice et al., 1994). In our study, two patients with Noonan’s syndrome had low BMD both at lumbar spine and neck of femur, which normalized after adjusting for body size. Similarly, the seven patients with Klinefelter’s syndrome had a slightly higher BMD (mean BMD at lumbar spine and neck of femur were 1-09 and 0-97 g/cm2), but they were also tall by a mean 4 cm. However, they were not significantly different when analysed separately. Thus it is always essential to evaluate BMD in relation to body size, especially with extreme short or tall stature.
It is also possible that the Klinefelter subgroup of patients also had less severe androgen deficiency, as half of these patients had normal pubertal onset with subsequent pubertal arrest. This might have permitted a relatively greater BMD.
There was a slightly lower areal BMD at neck of femur in the group of patients with secondary hypogonadism, although still within the adult normal range. Other investigators have reported decreased total bone mineral content in this group of hypogo- nadal men as compared to age-matched controls (Medras et al., 2000). Three of our patients in this group (two patients with Kall- man’s syndrome and one patient with hypopituitarism) were less than 22 years of age at the time of BMD measurement and therefore may not have reached peak BMD. It is possible that these values may further increase with time. Longitudinal data will be obtained for all patients.
This study, like many other studies in this area, suffers from the lack of a control group. The ethical issue of radiation exposure where adequate adult normal population data already exist, makes it difficult to establish a control group. This study also provides no baseline BMD data at the start of subcutaneous T implant therapy. As patients in our series were young and still growing when started on subcutaneous T implants, they had certainly not reached their peak bone mass. Baseline BMD studies would have yielded widely varying and uninterpretable information. A recent study of BMD and bone turnover with the use of transdermal T in hypogonadal men (Wang et al, 2001) provides a model for future studies in this area.
In summary, regular and adequate long-term subcutaneous T pellet implants in hypogonadal men result in adult BMD within the normal range expected for an age/gender-matched population. In addition to being safe and with an acceptable mode of delivery, subcutaneous T pellet implants are efficient and provide sustained physiological levels of T, with no changes in SHBG, and may thus contribute to increased androgenic effect at the receptor level.
Acknowledgements
Shankar Kanumakala was the Novo-Nordisk UK Fellow at Royal Children’s Hospital, Melbourne for 2001-02.
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