Serum uric acid values in various states of thyroid function

Thyroid hormones modulate uric acid metabolism in patients with recent onset subclinical hypothyroidism by improving insulin sensitivity

Some evidence suggests a relationship between thyroid dysfunction and uric acid (UA) metabolism, but the potential influential role of thyroid hormones on UA metabolism is still debated. This report was designed to evaluate the influential role of levothyroxine (L-T4) replacement therapy on circulating levels of UA in patients with recent onset post-thyroidectomy subclinical hypothyroidism. Circulating levels of thyroid hormones, UA and other metabolic parameters were assessed in 155 recently thyroidectomized patients (131 females, mean age 51.1 ± 12.7 years) at baseline (5-7 day after surgery) and after 2 months under replacement therapy with L-T4. At baseline, circulating levels of thyroid hormones were indicative of a subclinical hypothyroidism (TSH 8.2 ± 5.1 mU/mL, FT3 2.1 ± 0.7 pg/mL, FT4 9.2 ± 3.4 pg/mL). The mean serum UA concentration was 5.0 ± 1.3 mg/dL, while the prevalence of hyperuricemia, defined by serum UA levels > 6 mg/dL, was 22.6%. Serum UA levels at baseline were significantly correlated with HOMA-IR index (r = 0.475, p < 0.0001). After 2 months under the replacement therapy with L-T4, both serum UA levels (- 1.2 ± 0.9 mg/dL, p < 0.0001 vs. baseline) and HOMA-IR (- 0.3 ± 1.5 mmol/L, p = 0.0328 vs. baseline) significantly decreased. Multivariate regression analysis revealed that changes in HOMA-IR explained 23% of the variations of serum UA levels under L-T4 replacement therapy (β = 0.295, p < 0.0001, R² = 0.230). Our study suggests that thyroid hormones could modulate UA metabolism in patients with recent onset subclinical hypothyroidism likely by improving insulin sensitivity.

Osteoarticular disorders of endocrine origin

Endocrine diseases may present with musculoskeletal complaints, and their outcome, even after endocrine control, can be impaired by bone and joint disorders. All musculoskeletal structures, including bone, cartilage, synovium, tendons and ligaments, can be involved by some processes triggered by the endocrine disorder and its related disturbances of homeostasis, including that of growth factors. Endocrine disorders may account for 20-30% of all cases of osteopenia or osteoporosis in adults, the main causes being central and peripheral hypogonadism, endogenous and exogenous hypercorticism or hyperthyroidism, and primary hyperparathyroidism. The physician should be aware of these identifiable and treatable causes of bone loss when interpreting bone mineral density measurements. It is also valuable to evaluate bone status in patients diagnosed with these endocrine disorders. Specific bone therapeutic measures could be discussed. Other frequent musculoskeletal features include myopathy and joint and soft tissue involvement. Endocrine myopathy is frequent in most of the endocrine disorders and is non-specific since proximal painless muscle weakness associated with normal serum enzyme levels and an uncommonly encountered electromyogram myopathic pattern are present in these diseases. Soft tissue involvement is also a frequent consequence of acromegaly, hypothyroidism and diabetes mellitus. There is also a risk of nerve entrapment syndromes in these conditions. Specific arthropathies are the hallmark of acromegaly at the spinal and peripheral joints. Neuroarthropathies are a severe complication of diabetes mellitus as a result of infection, neuropathy and vasculopathy. In all these settings, the physician should be aware that endocrine disorders are part of the differential diagnosis and, conversely, that these articular and peri-articular lesions should be managed independently of the control of the underlying endocrine condition, a specific outcome being borne in mind.

The prevalence of hypothyroidism in gout

PURPOSE

To examine the potential relationship between gout and hypothyroidism.

PATIENTS AND METHODS

Fifty-four consecutive patients with a diagnosis of monosodium urate crystal-proven gouty arthritis on joint aspiration were prospectively evaluated for hypothyroidism with an ultrasensitive thyroid-stimulating hormone (TSH) assay. Twenty-five patients with a diagnosis of monosodium urate crystal-proven gout were retrospectively identified from a population of 137 patients receiving uric acid-lowering medications. These patients were also screened for hypothyroidism. Age, race, sex, and weight matched patients with noninflammatory rheumatic diseases and no history of gout served as controls. Hypothyroidism was diagnosed when a TSH was greater than 6.0 microU/mL or if a history of hypothyroidism requiring replacement therapy was documented.

RESULTS

The prevalence of hypothyroidism in the prospective group was significantly increased compared to controls (P < 0.05). Overall 15% of these patients, 25% of women and 12% of the men, had hypothyroidism. These rates were 2.5 times greater in women and 6 times greater in men than found in the controls. The mean TSH of the prospective gouty patients was also significantly greater than those levels found in control patients (5.2 +/- 12 versus 1.8 +/- 1.1 microU/mL, P < 0.05, chi-square), even when all abnormally elevated TSH values were excluded from analysis. The prevalence of hypothyroidism in the retrospective group was even higher: 20% overall, 40% in women and 15% in men.

CONCLUSIONS

The prevalence of hypothyroidism is significantly increased in patients with aspirate-proven gouty arthritis. Screening for hypothyroidism with an ultrasensitive thyroid-stimulating hormone assay should be considered in all patients presenting with gouty arthritis and those with a history of recurrent gouty flares.

Diuretic induced gout: a multifactorial condition

Fifteen patients with clinical gout occurring after long term treatment with diuretics were studied retrospectively. In all 15 patients one or more additional factors were present which might have contributed to the hyperuricaemia and gout. The most common of these was the impairment of the glomerular filtration rate. Twenty five other patients receiving long term treatment with diuretics who did not have gout were also studied. The concentrations of uric acid, urea, and creatinine were, in general, markedly lower in these patients than in those who had developed gout. It is concluded that diuretic induced gout occurs in patients in whom there is an additional cause of hyperuricaemia, usually impaired renal function.

Uric acid metabolism in children

The renal excretion of uric acid in children differs quantitatively, and perhaps qualitatively, from that in adult humans. The younger the child, the greater the renal clearance of uric acid and the greater the excretion of uric acid expressed as mg per kg body weight. During infancy, the reduced ability to maximally concentrate the urine may protect against precipitation of uric acid crystals within the kidney. Conversely, the extremely high urinary uric concentrations places the very small infant at jeopardy during sudden increases in the filtered load of uric acid. Understanding the pharmacologic and physiologic modulators of renal uric acid clearance will allow the pediatrician to minimize the risk of uric acid nephropathy, and to understand the implications of uric acid in the serum or urine in children with fluid and electrolyte disorders. Certainly evaluation of serum and urinary uric acid concentrations is essential in any child with acute renal failure.