Hyperparathyroidism is an endocrine and metabolic condition characterized by inappropriate or excessive secretion of parathyroid hormone (PTH) relative to the ionized calcium set point and the status of mineral metabolism. Under physiological conditions, PTH acts as a rapid regulator of calcium-phosphate homeostasis by modulating the kidneys, bone and, indirectly, the intestine through regulation of calcitriol synthesis. In hyperparathyroidism, this regulatory circuit loses its precision: hormone levels remain elevated or are not adequately suppressed, producing a biochemical and clinical profile that varies according to the underlying cause and organ reserve, particularly renal reserve.
From a clinical perspective, the concept is unified, but the principal forms differ in their mechanisms and outcomes. Primary hyperparathyroidism results from autonomous parathyroid secretion and tends to be associated with hypercalcemia. Secondary hyperparathyroidism represents an adaptive response to chronic stimuli such as chronic kidney disease or vitamin D deficiency, often with normal or low serum calcium. Tertiary hyperparathyroidism is the autonomous evolution of secondary hyperparathyroidism, typically after a long history of mineral metabolism disorders, and is characterized by hypercalcemia and advanced parathyroid hyperplasia. Early differentiation among these conditions is essential because their therapeutic goals, urgency and prognosis differ.
The epidemiology of hyperparathyroidism depends on the distribution of its principal forms and on how frequently serum calcium and PTH are measured in clinical practice. In the general population, the most commonly recognized cases are associated with primary hyperparathyroidism, which is often detected incidentally during blood testing or as part of the diagnostic evaluation of osteoporosis and nephrolithiasis. Prevalence increases with age and is higher among women, particularly after menopause, partly because of screening practices and partly because skeletal vulnerability makes the disease more evident through fractures, loss of bone mineral density or bone pain.
In current clinical practice, primary hyperparathyroidism is no longer, in most cases, an overt disease presenting with osteitis fibrosa cystica. It more often encompasses a spectrum ranging from paucisymptomatic or asymptomatic forms to clinically complex disease. This epidemiological transition is related to the early detection of mild hypercalcemia and increased attention to markers of target-organ risk. In parallel, the concept of normocalcemic primary hyperparathyroidism has emerged. In this condition, serum calcium remains within the reference range while PTH is persistently elevated after rigorous exclusion of secondary causes. Its estimated epidemiological burden therefore depends substantially on the quality of the diagnostic assessment and on the exclusion criteria applied.
Secondary hyperparathyroidism is instead predominantly associated with chronic kidney disease (CKD) and the related mineral and bone disorders. Its frequency increases as glomerular filtration rate declines and with prolonged exposure to relative hyperphosphatemia, reduced calcitriol synthesis and functional hypocalcemia. In this setting, elevated PTH initially represents an attempt to preserve calcium and phosphate homeostasis, but over time it may become a determinant of pathological bone remodeling and extraskeletal calcification, particularly when accompanied by persistent phosphate and calcium abnormalities.
Risk factors vary according to etiology. In primary hyperparathyroidism, in addition to age and sex, family history and the presence of rare genetic syndromes are relevant, because hyperparathyroidism may represent the first sign of a broader disorder. Certain pharmacological exposures require particular attention. Lithium can alter the calcium-sensing receptor set point and promote hyperparathyroidism with hypercalcemia. Thiazide diuretics may increase serum calcium and unmask pre-existing disease. Unbalanced calcium and vitamin D supplementation may complicate interpretation of laboratory values and the clinical course in predisposed patients.
In secondary hyperparathyroidism, the principal determinants are CKD progression, the quality of phosphate control, vitamin D status and the presence of chronic inflammation, malnutrition or malabsorption, all of which amplify the parathyroid response. Even in the absence of CKD, vitamin D deficiency and reduced calcium intake can sustain a chronic increase in PTH, with particular clinical relevance when associated with skeletal fragility. Overall vulnerability also depends on the patient’s renal and skeletal reserve. Cardiovascular comorbidities, previous nephrolithiasis, osteoporosis and frailty increase the clinical burden of hyperparathyroidism even when biochemical abnormalities are moderate.
PTH physiology is based on a finely regulated control system. Small variations in ionized calcium rapidly modulate parathyroid secretion through the calcium-sensing receptor (CaSR). When serum calcium decreases, PTH rises and acts on the kidneys and bone to restore calcium levels, while lowering serum phosphate by increasing urinary phosphate excretion. At the same time, PTH stimulates renal 1-alpha-hydroxylase, increasing the production of calcitriol, which enhances intestinal absorption of calcium and phosphate. Hyperparathyroidism develops when this circuit is driven by glandular autonomy or by chronic stimuli that cause a persistent increase in PTH.
From an etiological perspective, primary hyperparathyroidism is caused mainly by a solitary parathyroid adenoma, less commonly by multiglandular hyperplasia and rarely by parathyroid carcinoma. The common denominator is PTH secretion that is not adequately suppressible by hypercalcemia, with loss of the normal relationship between serum calcium and hormone output. In certain pharmacological conditions, particularly during lithium treatment, the suppression set point is increased. The CaSR perceives a higher calcium concentration as normal, promoting persistently elevated PTH and a tendency toward hypercalcemia. Primary hyperparathyroidism may also occur as part of genetic syndromes in which a predisposition to parathyroid proliferation coexists with other endocrine disorders, making it essential to identify suggestive clinical and familial features.
Secondary hyperparathyroidism is an adaptive response to prolonged stimuli. In CKD, reduced phosphate excretion promotes phosphate retention and a reduction in ionized calcium, while nephron loss decreases calcitriol synthesis and consequently intestinal calcium absorption. These abnormalities are accompanied by changes in bone signaling and regulation of fibroblast growth factor 23 (FGF23), producing a complex biochemical profile in which increased PTH attempts to maintain serum calcium and limit serum phosphate, but at the cost of accelerated bone remodeling and, in advanced stages, progressive parathyroid hyperplasia. Over time, the glands may become less sensitive to calcium and inhibitory signals, creating the conditions for progression toward functional autonomy.
Tertiary hyperparathyroidism represents this transition. After a long history of secondary hyperparathyroidism, often in patients receiving long-term dialysis or following kidney transplantation, the hyperplastic parathyroid tissue acquires relatively autonomous secretion and may maintain elevated PTH even after the mineral balance has improved. In these cases, hypercalcemia again becomes a central feature, with a clinical profile combining chronic target-organ damage and acute risks related to elevated serum calcium.
The pathophysiology of PTH excess involves bone and the kidneys in an integrated manner. In bone, PTH increases resorption by activating the receptor activator of nuclear factor kappa-B ligand (RANKL) pathway in stromal cells and osteoblasts, thereby increasing osteoclast formation and activity. In persistent forms, this process causes loss of bone mass, particularly cortical bone, with an increased risk of fractures and, in the most severe cases, osteitis fibrosa cystica. In the kidneys, PTH increases calcium reabsorption in the distal tubule and reduces phosphate reabsorption in the proximal tubule, promoting phosphaturia. However, when hypercalcemia is persistent, the filtered calcium load and urinary calcium excretion increase, raising the risk of nephrolithiasis and nephrocalcinosis, with possible progressive impairment of renal function.
Systemic consequences depend on the combined effects of PTH, calcium and phosphate. In primary hyperparathyroidism, hypercalcemia may cause polyuria and polydipsia because of impaired urinary concentrating ability, as well as gastrointestinal symptoms, fatigue and neurocognitive changes. In CKD, the predominant risk is often related to the interaction among elevated PTH, phosphate and calcium, with consequences for bone and the cardiovascular system, because mineral and bone disorder is associated with vascular and valvular calcification and with a risk profile that cannot be explained by serum calcium alone. This complexity requires an approach that integrates mechanism, biochemical severity and target-organ vulnerability, avoiding interpretation of an isolated PTH value.
The clinical presentation of hyperparathyroidism is highly variable and depends on both its etiology and the severity and duration of mineral abnormalities. In primary hyperparathyroidism, many diagnoses are now made at an early stage, when symptoms are mild or absent and hypercalcemia is detected incidentally. However, the absence of an overt clinical picture does not imply clinical irrelevance, because even mild chronic forms may be associated with nephrolithiasis, reduced bone mineral density and functional decline. In secondary hyperparathyroidism, particularly in CKD, symptoms may be dominated by bone pain, pruritus, muscle cramps and fragility, but they often overlap with uremic symptoms and comorbidities, making a structured interpretation of the clinical context essential.
During medical history taking, patients with primary hyperparathyroidism frequently report nonspecific symptoms such as fatigue, reduced physical performance, sleep disturbances and difficulty concentrating, sometimes associated with depressed mood or irritability. Urinary symptoms require particular attention. Renal colic, recurrent nephrolithiasis, polyuria and increased thirst may indicate chronic hypercalcemia. Gastrointestinal manifestations may include nausea, constipation and dyspepsia, while neuromuscular manifestations may include proximal muscle weakness and myalgia, particularly when vitamin D deficiency and sarcopenia coexist.
The physical examination is often poor in specific findings, but it should focus on signs of dehydration, reduced muscle tone and bone tenderness, as well as manifestations of complicated nephrolithiasis. Skeletal assessment requires a clinical approach. A history of fragility fractures, height loss or back pain may suggest vertebral fractures, even in the absence of significant trauma. In patients with CKD and advanced secondary hyperparathyroidism, more evident signs of bone disease may emerge, including diffuse pain, reduced mobility and marked skeletal fragility.
Hyperparathyroidism may be associated with acute manifestations when serum calcium rises rapidly or reaches very high levels. In these cases, patients may develop drowsiness, confusion, nausea, vomiting and rapid deterioration in general condition, accompanied by marked polyuria and dehydration. This presentation, which is more typical of severe hypercalcemia, represents a transition from chronic disease to the risk of hypercalcemic crisis, in which clinical stabilization becomes the priority before complete etiological characterization.
Overall, the clinical manifestations of hyperparathyroidism cannot be reduced to a list of symptoms, because their relevance depends on the combination of biochemical abnormalities, target-organ damage and patient vulnerability. A coherent assessment must therefore relate a history of nephrolithiasis, skeletal fragility and neurocognitive symptoms to the profile of calcium, PTH, phosphate, vitamin D and renal function, while already anticipating the therapeutic implications.
Hyperparathyroidism should be suspected when PTH is elevated or inappropriately normal in the presence of abnormal serum calcium, or when typical clinical conditions suggest a disorder of mineral metabolism. The most common context is incidentally detected hypercalcemia. In this setting, PTH is the key variable for distinguishing PTH-mediated hypercalcemia from conditions in which PTH is suppressed. When serum calcium is elevated and PTH is not reduced, primary or tertiary hyperparathyroidism becomes the principal diagnostic consideration and requires prompt assessment to prevent renal and skeletal complications.
Clinical suspicion should be high in patients with recurrent nephrolithiasis, nephrocalcinosis or progressive unexplained loss of renal function, particularly when hypercalcemia, hypercalciuria or phosphate abnormalities coexist. Similarly, in patients with osteoporosis, fragility fractures, subclinical vertebral fractures or a marked reduction in bone mineral density, measurement of calcium and PTH is strategically important because it may identify a reversible or modifiable cause of bone loss and guide the appropriate therapeutic choice.
In internal medicine and nephrology practice, secondary hyperparathyroidism should be suspected in patients with chronic kidney disease (CKD) when PTH rises progressively, particularly when accompanied by hyperphosphatemia or signs of mineral and bone disorder. In this context, suspicion does not depend on a single isolated value, but on a trajectory. The trend in PTH over time, interpreted in relation to calcium, phosphate and vitamin D, defines the likelihood of high-turnover bone disease and guides treatment intensity.
Another relevant scenario is the presence of nonspecific symptoms consistent with hypercalcemia or mineral imbalance. Polyuria, thirst, constipation, nausea, fatigue and cognitive difficulties may be manifestations of even mild chronic hypercalcemia. Suspicion should be strengthened by predisposing factors such as lithium use, a history of vitamin D deficiency, malabsorption, an unbalanced calcium-restricted diet, and a family history of parathyroid disorders or multiple endocrine syndromes.
Finally, in the presence of rapid deterioration in general condition associated with dehydration, altered mental status and severe hypercalcemia, the differential diagnosis must include hypercalcemic crisis and requires urgent stabilization. Although the underlying cause may vary, severe primary hyperparathyroidism, tertiary hyperparathyroidism and parathyroid carcinoma are among the diagnoses that should be considered as priorities when PTH is elevated and serum calcium is markedly increased.
The diagnosis of hyperparathyroidism requires a rational sequence that confirms the biochemical abnormality, defines its mechanism and quantifies target-organ damage. The first step is measurement of serum calcium, preferably corrected for albumin or assessed as ionized calcium when appropriate, together with measurement of PTH using a reliable assay. Interpretation must be contextual. Elevated PTH in the presence of hypercalcemia is inappropriate and suggests a PTH-mediated disorder, whereas suppressed PTH in hypercalcemia directs the diagnosis toward non-parathyroid causes. When serum calcium is normal and PTH is elevated, the key issue is distinguishing normocalcemic primary hyperparathyroidism from secondary hyperparathyroidism, avoiding premature diagnoses that could lead to unnecessary or ineffective treatment.
The evaluation should include serum phosphate, creatinine with estimated glomerular filtration rate, 25-hydroxyvitamin D and, when useful, bone turnover markers. Vitamin D is a crucial interpretative factor. Deficiency may sustain elevated PTH and should be corrected before diagnosing normocalcemic primary hyperparathyroidism. Renal function also influences both physiology and interpretation, because in CKD PTH may increase as an adaptive response and the diagnostic framework shifts from primary hyperparathyroidism toward CKD-related mineral and bone disorder.
Diagnostic assessment of hyperparathyroidism
A decisive diagnostic step is distinguishing primary hyperparathyroidism from familial hypocalciuric hypercalcemia, because both conditions may present with hypercalcemia and nonsuppressed PTH but require different management strategies. Evaluation of urinary calcium excretion and derived indices, together with family history and stability of the biochemical profile over time, helps prevent inappropriate surgery. Similarly, recognition of non-PTH-mediated hypercalcemia is based on PTH suppression and a differential diagnostic pathway that includes malignancy, vitamin D excess, granulomatous diseases and other endocrine conditions, making PTH a fundamental initial diagnostic discriminator.
In primary hyperparathyroidism, parathyroid imaging is not a diagnostic test, but a tool for preoperative localization. Neck ultrasonography, sestamibi scintigraphy and advanced techniques such as four-dimensional computed tomography are used to plan a targeted surgical approach, particularly when minimally invasive parathyroidectomy is intended. Imaging should therefore be requested when the therapeutic decision is directed toward surgery, avoiding its premature use or its interpretation as a substitute for biochemical reasoning.
In secondary and tertiary hyperparathyroidism associated with CKD, diagnosis is integrated into the broader context of mineral and bone disorder. Assessment is based on trends in PTH, calcium and phosphate in relation to treatment, dialysis and nutritional status. Characterization of the bone phenotype may require specific investigations in selected cases, but in most patients the diagnostic pathway is intended to guide treatment and prevent skeletal and cardiovascular complications rather than to identify a single localizable lesion.
The classification of hyperparathyroidism links the underlying mechanism to the therapeutic strategy. The fundamental distinction is among primary, secondary and tertiary hyperparathyroidism.
Within primary hyperparathyroidism, a clinically relevant form is normocalcemic primary hyperparathyroidism, defined by persistently elevated PTH with repeatedly normal serum calcium after careful exclusion of secondary causes and confounding factors. This category requires diagnostic rigor because inappropriate application of the definition may transform vitamin D deficiency or malabsorption into a diagnosis of parathyroid autonomy. When correctly identified, the normocalcemic phenotype may nevertheless be associated with reduced bone mineral density or nephrolithiasis and is therefore not necessarily benign.
Another practical classification concerns the presence of complications and the degree of risk. Low-impact forms, characterized by mild biochemical abnormalities and no target-organ damage, can be distinguished from high-impact forms in which significant hypercalcemia, nephrolithiasis, reduced glomerular filtration rate, osteoporosis or vertebral fractures coexist. In these forms, etiological correction has clearer prognostic value because it reduces the likelihood of progressive renal damage and further skeletal events.
Severity also includes the dynamics of serum calcium. Slowly progressive hypercalcemia may be clinically tolerated but cause cumulative damage, whereas a rapid increase in serum calcium may precipitate acute manifestations with dehydration and neurocognitive impairment. This aspect is particularly important when assessing the risk of hypercalcemic crisis and the need for urgent stabilization before definitive intervention.
Finally, certain rare forms have specific clinical implications. Parathyroid carcinoma, although uncommon, may cause severe recurrent hypercalcemia with markedly elevated PTH and requires a dedicated specialist pathway. Genetic and syndromic forms require a classification that considers the risk of multifocal disease and recurrence, together with more intensive follow-up. In all cases, an effective classification is one that translates pathophysiology into a concrete and individualized management plan.
Treatment of hyperparathyroidism depends directly on its etiology and its impact on target organs. In primary hyperparathyroidism, the goal is to reduce PTH excess and prevent or limit renal and skeletal complications. Parathyroidectomy is the definitive treatment when indicated, with high efficacy in normalizing serum calcium and PTH and improving bone mineral density over time. The decision to perform surgery cannot be based solely on subjective symptoms because many forms are paucisymptomatic. It must integrate serum calcium levels, skeletal status, renal function, history of nephrolithiasis and the overall risk profile. Accurate preoperative localization enables targeted strategies, but the indication for surgery remains based on clinical and biochemical criteria and the risk of disease progression.
When surgery is not indicated or cannot be performed, medical treatment aims to control serum calcium and protect bone. Calcimimetics reduce PTH secretion by increasing CaSR sensitivity and are particularly useful for controlling hypercalcemia, while antiresorptive therapies may be used to improve bone mineral density in selected patients, with careful consideration of efficacy, risk and renal function. Correction of vitamin D deficiency is a cross-cutting component of management. It should be pursued cautiously and with appropriate monitoring because it reduces the parathyroid stimulus but may increase serum calcium in some patients. The practical goal is to prevent deficiency from amplifying PTH secretion and worsening skeletal fragility without promoting persistent hypercalcemia.
In secondary hyperparathyroidism caused by CKD, the strategy differs. The principal objective is to control mineral and bone disorder by managing phosphate, vitamin D and PTH secretion, thereby reducing pathological bone remodeling and extraskeletal complications. Management includes restriction of dietary phosphate and targeted use of phosphate binders, together with vitamin D analogues or vitamin D receptor activators when appropriate, while balancing the risk of hypercalcemia and hyperphosphatemia. Calcimimetics have an important role, particularly in patients receiving dialysis, because they reduce PTH and, in some cases, serum calcium and phosphate, contributing to biochemical control. In refractory forms associated with advanced hyperplasia and markedly elevated PTH, parathyroidectomy may become necessary to achieve clinical control and reduce the burden of complications.
In tertiary hyperparathyroidism, often occurring after kidney transplantation or after a long history of CKD, treatment must address acquired autonomy. Control of serum calcium is central because hypercalcemia may impair renal function and increase the risk of calcification. In this setting, calcimimetics may be used as a bridging treatment or when surgery is not feasible, but parathyroidectomy often remains the most definitive treatment for autonomous disease associated with persistent hypercalcemia and target-organ damage.
A common aspect of management is the treatment of severe hypercalcemia. When serum calcium is markedly elevated or the patient is symptomatic, the priority is stabilization with hydration and interventions that rapidly lower serum calcium, selected according to severity and underlying cause. When hypercalcemia persists, etiological correction should not be delayed. In severe primary hyperparathyroidism, rapid definition of the surgical or specialist pathway reduces the risk of recurrence and multisystem complications. In all cases, an effective strategy integrates the immediate objective of patient safety with the long-term objective of controlling the source of elevated PTH.
Follow-up of hyperparathyroidism should ensure biochemical stability, prevention of complications and assessment of treatment effectiveness over time. In surgically treated primary hyperparathyroidism, early monitoring includes serum calcium and PTH to confirm resolution and identify transient hypocalcemia or hungry bone syndrome in patients with high preoperative bone turnover. During the subsequent phase, follow-up aims to document skeletal recovery and prevent recurrence, particularly in multiglandular or syndromic forms.
In patients managed conservatively or receiving medical treatment, periodic monitoring of calcium, PTH, phosphate, renal function and vitamin D is essential because the condition may evolve and because treatment modifies mineral balance. Interpretation must remain consistent with the underlying mechanism. In primary hyperparathyroidism, serum calcium is the principal determinant of immediate risk and PTH reflects disease activity. In secondary hyperparathyroidism associated with CKD, the PTH trajectory in relation to calcium and phosphate is more informative than an isolated value and guides treatment intensity.
Renal follow-up has a central role. In patients with a history of nephrolithiasis or hypercalciuria, targeted clinical and imaging surveillance is useful for identifying recurrent stones or nephrocalcinosis and adapting preventive strategies. Renal function should be monitored over time because primary hyperparathyroidism may be associated with reduced glomerular filtration and because, in CKD, the objective is to limit progression of mineral and bone disorder, which amplifies skeletal fragility and cardiovascular risk.
Skeletal monitoring should include bone densitometry at intervals appropriate to the individual risk profile and the intervention performed. After correction of primary hyperparathyroidism, a gradual recovery in bone mineral density is expected, but its trajectory depends on age, vitamin D status, calcium intake, physical activity and the presence of other causes of osteoporosis. In patients with CKD, assessment of skeletal risk requires cautious interpretation and integration with the biochemical profile because the relationship between bone density and bone turnover may differ from that observed in the general population.
Finally, follow-up should be structured as continuity of care. It should include patient education regarding the symptoms of hypercalcemia and hypocalcemia, treatment adherence, management of diet and interfering medications, and definition of thresholds requiring prompt reassessment. Structured monitoring reduces the probability of renal and skeletal complications and enables early modification of the therapeutic plan when disease severity or phenotype changes.
The prognosis of hyperparathyroidism is favorable when the underlying cause is correctly identified and treatment is directed at the mechanism, but it depends substantially on the duration of exposure and the degree of target-organ damage at diagnosis. In primary hyperparathyroidism, parathyroidectomy, when indicated, generally normalizes serum calcium and reduces the risk of progressive skeletal and renal damage. However, complications are not uniformly reversible. Recovery of bone mineral density requires time, while nephrolithiasis may recur if lithogenic factors unrelated to PTH persist. In older patients or those with CKD, reduced organ reserve increases the clinical relevance of even moderate biochemical abnormalities because they amplify the risk of fractures and renal events.
The principal complications of primary hyperparathyroidism are nephrolithiasis, nephrocalcinosis and reduced renal function, together with osteoporosis and fractures. Skeletal involvement results from accelerated remodeling and predominant loss of cortical bone, producing a pattern of fragility that may also manifest as clinically unrecognized vertebral fractures. Neurocognitive and neuromuscular manifestations, although less specific, may substantially impair quality of life and independence, particularly when associated with sarcopenia and physical deconditioning.
In secondary hyperparathyroidism associated with CKD and in tertiary hyperparathyroidism, complications include high-turnover bone disease, bone pain, fractures and a substantial burden of vascular and valvular calcification, in a setting in which calcium and phosphate interact with PTH and bone-derived regulators. In these patients, prognosis is often determined by the underlying kidney disease, but suboptimal control of mineral and bone disorder worsens fragility, hospitalization rates and cardiovascular risk, making treatment of elevated PTH an integral part of comprehensive management.
A specific clinical risk is severe hypercalcemia associated with dehydration and altered mental status, which may progress to a hypercalcemic crisis with acute renal impairment and cardiac instability. This scenario is more likely when serum calcium is markedly elevated or rises rapidly and requires urgent stabilization followed by correction of the underlying cause. Treatment-related complications must also be considered. After parathyroidectomy, transient hypocalcemia, hungry bone syndrome and, more rarely, recurrent laryngeal nerve injury may occur. Medical therapies require monitoring to prevent hypocalcemia, hyperphosphatemia or deterioration of renal function, depending on the treatment and clinical context.
Overall, hyperparathyroidism is a condition in which prognosis depends on the quality of the etiological assessment and the ability to prevent progressive target-organ damage. A pathway integrating biochemical evaluation, renal and skeletal assessment and individualized treatment enables effective control in most cases and significantly reduces the risk of long-term complications.