Thyroid abnormalities in patients with myotonic dystrophy

Predicting daytime sleepiness and fatigue: a 9-year prospective study in myotonic dystrophy type 1

OBJECTIVE

Daytime sleepiness and fatigue are prominent symptoms of myotonic dystrophy type I (DM1) that exact a heavy toll on patients' quality of life, but information is scarce on their predictive factors. This study aimed to determine factors that may influence levels of daytime sleepiness and fatigue in a large cohort of DM1 patients followed for 9 years.

METHODS

This study included 115 patients with DM1 at baseline (Time 1, T1) and at Time 2 (T2) who were questioned for daytime sleepiness, fatigue, history of depression, psychological distress, pain, hypothyroidism, and sleep habits. Also, their muscular impairment and intellectual quotient were evaluated. Regression models were used to identify correlates of daytime sleepiness and fatigue while controlling for time effect.

RESULTS

Both daytime sleepiness and fatigue increased between T1 and T2, but their rate of change are higher when CTG repeat number is higher (p < 0.05). Also, higher psychological distress level is associated with higher daytime sleepiness and fatigue levels both at T1 and T2 (p < 0.01). Moreover, patients with a history of depression report higher daytime sleepiness levels both at T1 and T2 (p < 0.05). In addition, patients with higher fatigue levels both at T1 and T2 have more severe muscular impairment (p < 0.01) and report a longer habitual sleep duration (p < 0.05). Finally, a higher BMI and a history of hypothyroidism predict higher daytime sleepiness levels at T2 (p < 0.05).

CONCLUSION

This study identified potentially modifiable risk factors of future daytime sleepiness and fatigue in DM1 patients, including BMI, psychological distress, hypothyroidism, and sleep habits.

Primary Hyperparathyroidism and Hyperthyroidism in a Patient with Myotonic Dystrophy: A Case Report and Review of the Literature

Various endocrine manifestations are commonly described in myotonic dystrophy (MD), including primary hypogonadism, diabetes mellitus, and thyroid and parathyroid dysfunction. We describe a 46-year-old woman with a family history of MD with her son. She was diagnosed with cardiac arrhythmia and required the implantation of a pacemaker. She was noted to have a bilateral cataract. She complained of muscle weakness, diffuse myalgia, and palpitation. The electromyography (EMG) showed myotonic discharges. Laboratory tests showed high serum calcium 2.83 mmol/L, serum phosphate 1.2 mmol/L, parathormone 362.5 pg/mL, thyroid stimulating hormone TSH 0.02 mIU/L (normal range: 0.34–5.6 mIU/L), FT4 21.17 ng/mL, and negative anti-thyroperoxidase antibodies. Cervical ultrasound revealed a multinodular goiter. The 99mTc-MIBI scintigraphy localized a lower right parathyroid adenoma. The clinical data, the family history of MD, EMG data, and endocrine disturbances were strongly suggestive of MD associated with hyperthyroidism and primary hyperparathyroidism.

Endocrine function in 97 patients with myotonic dystrophy type 1

The aim of this study was to investigate the endocrine function and its association to number of CTG repeats in patients with myotonic dystrophy type 1 (DM1). Concentration of various hormones and metabolites in venous blood was used to assess the endocrine function in 97 patients with DM1. Correlation with CTG(n) expansion size was investigated with the Pearson correlation test. Eighteen percent of the DM1 patients had hyperparathyroidism with increased PTH compared with 0.5% in the background population. Of these, 16% had normocalcemia and 2% had hypercalcemia. An additional 3% had hypercalcemia without elevation of PTH; 7% had abnormal TSH values (2% subnormal and 5% elevated TSH levels); 5% of the patients had type 2 diabetes mellitus; 17% of the male DM1 patients had increased LH and low levels of plasma testosterone indicating absolute androgen insufficiency. Another 21% had increased LH, but normal testosterone levels, indicating relative insufficiency. Numbers of CTG repeats correlated directly with plasma PTH, phosphate, LH, and tended to correlate with plasma testosterone for males. This is the largest study of endocrine dysfunction in a cohort of Caucasian patients with DM1. We found that patients with DM1 have an increased risk of abnormal endocrine function, particularly calcium metabolism disorders. However, the endocrine dysfunction appears not to be of clinical significance in all of the cases. Finally, we found correlations between CTG(n) expansion size and plasma PTH, phosphate, and testosterone, and neck flexion strength.

Increased cancer risks in myotonic dystrophy

OBJECTIVE

To estimate cancer risks for patients with myotonic dystrophy, given that increased risks for neoplasms in association with myotonic dystrophy type 1 and type 2 have been suggested in several studies but the risks of cancers have not been quantified.

PATIENTS AND METHODS

A cohort of 307 patients with myotonic dystrophy identified from medical records of Mayo Clinic in Rochester, MN, from January 1, l993, through May 28, 2010, was retrospectively analyzed. We estimated standardized incidence ratios (SIRs) of specific cancers for patients with myotonic dystrophy compared with age- and sex-specific cancer incidences of the general population. Age-dependent cumulative risks were calculated using the Kaplan-Meier method.

RESULTS

A total of 53 cancers were observed at a median age at diagnosis of 55 years. Patients with myotonic dystrophy had an increased risk of thyroid cancer (SIR, 5.54; 95% confidence interval [CI], 1.80-12.93; P=.001) and choroidal melanoma (SIR, 27.54; 95% CI, 3.34-99.49; P<.001). They may also have an increased risk of testicular cancer (SIR, 5.09; 95% CI, 0.62-18.38; P=.06) and prostate cancer (SIR, 2.21; 95% CI, 0.95-4.35; P=.05). The estimated cumulative risks at age 50 years were 1.72% (95% CI, 0.64%-4.55%) for thyroid cancer and 1.00% (95% CI, 0.25%-3.92%) for choroidal melanoma. There was no statistical evidence of an increased risk of brain, breast, colorectal, lung, renal, bladder, endometrial, or ovarian cancer; lymphoma; leukemia; or multiple myeloma.

CONCLUSION

Patients with myotonic dystrophy may have an increased risk of thyroid cancer and choroidal melanoma and, possibly, testicular and prostate cancers.

Myotonic dystrophy associated with variable circadian rhythms of serum cortisol and isolated thyrotropin deficiency

We describe a case of myotonic dystrophy presenting with a disturbed circadian rhythm of the serum cortisol and an isolated thyrotropin deficiency. The diagnosis of myotonic dystrophy was based on clinical characteristics, positive electromyographic findings, and increased number of CTG repeats in the dystrophia myotonica protein kinase (DMPK) gene. The patient presented with a variable circadian rhythm of the serum cortisol, increased excretion of urinary free cortisol, and a high adrenocorticotropin hormone responses to corticotropin-releasing hormone. The basal serum thyrotropin concentration was low and did not increase after thyrotropin-releasing hormone stimulation. The protein encoded by the DMPK gene may act as a second messenger in signal transduction, like a protein kinase. The present patient had a diverse pattern of disturbances in the hypothalamus-pituitary-endocrine organ axis, probably mediated by differences in the action or expression of the gene products in each endocrine cell.

Primary hyperthyroidism and associated hyperparathyroidism in a patient with myotonic dystrophy: Steinert with hyperthyroidism and hyperparathyroidism

A patient with myotonic dystrophy and associated primary hyperthyroidism and hyperparathyroidism is described; this association has not been reported previously, to the authors' knowledge. The patient also suffered from hypergonadotropic hypogonadism and hyperinsulinism with insulin resistance. The etiology of hyperthyroidism and hyperparathyroidism is not clear. At surgery, a parathyroid adenoma was extirpated, and a subtotal thyroidectomy was performed. Postoperative course was unremarkable, with consistently normal serum calcium levels but persistently elevated serum parathyroid hormone concentrations. The possibility that the patient had a residual hyperparathyroidism could not be eliminated. Thyroid function was normal. After surgery, the patient reported subjective improvement in his muscle strength. The authors conclude that both diseases-- hyperthyroidism and hyperparathyroidism--exert a negative effect on the myotonic dystrophy and that an early recognition of these two diseases is crucial for the favorable evolution of the patient.

Adrenocorticotropin hyperresponsiveness in myotonic dystrophy following oral fenfluramine administration

Abstract The plasma immunoreactive adrenocorticotropin and cortisol responses to oral fenfluramine hydrochloride (1.5mg/kg body wt) or placebo were examined in 11 patients with myotonic dystrophy, 4 controls with facioscapulohumeral dystrophy, a similarly debilitating muscle wasting disease, and 14 normal controls in single-blind studies performed in mid-afternoon. Mean areas under the adrenocorticotropin response versus time curve were significantly greater in myotonics (2573 + 429 pmol.min/L) than in facioscapulohumeral dystrophy controls (696 + 279 pmol.min/L, P<0.02) and normals (560+/-61 pmol.min/L, P<0.0001). Corresponding cortisol responses were significantly greater in myotonics (35757 + 3949 nmol.min/L) than in normals (21828+/-1669 nmol.min/L, P < 0.001), but not significantly greater than those in facioscapulohumeral dystrophy controls (22830 + 6140 nmol.min/L, P = 0.055). No stressful side-effects which could affect hormone responses, and no significant changes in blood pressure or heart rate were noted. Fenfluramine activates central serotonergic and/or noradrenergic pathways initiating secretion of corticotropin-releasing hormone and possibly arginine vasopressin. We postulate that these fenfluramine-activated pathways are hyperstimulated in myotonics, leading to adrenocorticotropin and cortisol hypersecretion. This may be a manifestation of a general cell membrane defect in myotonic dystrophy. We found a lack of correlation of age (and severity of disease) with adrenocorticotropin response in myotonics, and therefore, the hyperresponse may serve as a useful marker for the disease before development of other overt signs.

Thyroid function in patients with myotonic dystrophy

In order to investigate endocrine disturbances in patients with myotonic dystrophy (MD), 12 patients and 20 normal controls were studied. All patients were clinically euthyroid and there were no significant differences between circulating levels (mean +/- SD) of T4 (114.7 +/- 26.8 vs 129.9 +/- 28.3 nmol/l), FT4 (16.6 +/- 4.5 vs 18.4 +/- 3.8 pmol/l), T3 (1.61 +/- 0.29 vs 1.86 +/- 0.33 pmol/l), TSH (2.7 +/- 1.3 vs 2.4 +/- 1.4 mU/l), TBG (26.7 +/- 5.5 vs 27.6 +/- 4.9 mg/l), T4/T3 (84.3 +/- 18.4 vs 82.1 +/- 15.3), and FT4/FT3 (0.28 +/- 0.05 vs 0.33 +/- 0.08). Serum FT3 (4.3 +/- 1.4 pmol/l) in patients were significantly lower than those (5.3 +/- 0.9 pmol/l) in normal controls (P less than 0.02). Thyroidal 131I-uptakes (8.7 +/- 4.3%) in patients were significantly lower than those (25.8 +/- 7.4%) in controls (P less than 0.01). The mean maximal TSH responses following TRH stimulation were significantly less in patients with MD (11.4 +/- 4.5 vs 17.0 +/- 6.2 mU/l; P less than 0.02). Neither circulating thyroid microsomal nor thyroglobulin antibodies were detectable in the 11 patients tested. Serum thyroglobulin concentrations were within the normal range in all patients but one. In conclusion, it is suggested that normal levels of serum T4, T3, FT4, TSH, TBG, T4/T3 and FT4/FT3, slight but significant decrease of serum FT3, reduced TSH response to TRH and a decrease of thyroidal radioiodine uptake might be due to a slight functional failure of TSH secretion in patients with myotonic dystrophy.

Study of endocrine function in myotonic dystrophy

Endocrine function was studied in 12 patients, 7 men and 5 women, with myotonic dystrophy (MD). Growth hormone (GH) was within normal limits in all the patients and there was no response to arginine stimulation. Prolactin (PRL) was above normal in only 2 cases (one man and one woman) and the response to TRH was below normal in 2 patients and slightly above in one. The GnRH test yielded a reduced LH response in 4 of the 7 men and none at all in the 4 women in whom it was done. The FSH response was below normal in only one of the 7 men and in 3 out of 4 women. The testosterone assay after HCG stimulation was borderline high in 2 out of 6 men and below normal in one. The level of thyroid hormones (T3, T4, FTI, TSH) was normal in all patients except one, whose FTI and T4 level were below normal. In the TRH test TSH was raised in only one of the 6 patients tested. The circadian rhythm of cortisol was absent in 3 out of 10 patients and 3 out of 8 patients showed no response to ACTH stimulation. The results of the study suggest that endocrine alterations are fairly frequent in MD but that they are neither specific nor correlated with disease severity or duration.