Pathogenesis and classification
Bone mass peaks around 25 years of age. After 50 years, physiological bone loss begins (0.5–1% per year), but in osteoporosis, the annual loss accelerates to 3–5%. Due to impaired remodeling processes, resorption outpaces the formation of new bone.
The disease is divided into two major groups:
- Primary osteoporosis: includes postmenopausal (type 1, associated with estrogen deficiency), senile (type 2, associated with vitamin D deficiency), as well as the rare juvenile and idiopathic forms.
- Secondary osteoporosis: develops as a complication of other pathologies (endocrine, rheumatic, renal, and gastrointestinal diseases) or due to iatrogenic factors. The most common cause of secondary osteoporosis is corticosteroid therapy—signs of bone mass reduction can appear as early as one year after starting such treatment.
Clinical presentation
Osteoporosis is called the "silent epidemic" due to its long asymptomatic period. Diagnosis is often made only after a fracture occurs or as an incidental finding on an X-ray.
Main manifestations:
- Pain syndrome: diffuse bone pain (resulting from microfractures), worsening with physical exertion or percussion. Acute attacks develop later due to vertebral compression fractures.
- Changes in posture (Habitus): development of pronounced thoracic kyphosis ("round back"), shortening of the trunk, and skin folds on the abdomen.
- Anthropometric markers: the patient's arm span is approximately equal to their original height, and the distance from the crown to the symphysis pubis becomes more than 5 cm shorter than the distance from the symphysis to the soles of the feet.
Important nuance: neurological symptoms are extremely rare in osteoporotic vertebral compression fractures. If a patient presents with neurological deficits, this is a red flag necessitating the exclusion of metastases.
Diagnostics
Standard radiography has low sensitivity in the early stages. Radiologists cannot make a definitive diagnosis from an X-ray, describing only "decreased shadow density" or "atrophied trabecular pattern."
The gold standard is bone densitometry (measurement of bone mineral density — BMD). A BMD decrease of just 10–14% doubles the fracture risk. Results are evaluated using the T-score (in standard deviations from the peak bone mass norm):
- Normal: deviation < 1;
- Osteopenia: between 1 and 2.5;
- Osteoporosis: > 2.5.
Additionally, laboratory tests (assessment of calcium-phosphorus metabolism and bone turnover markers) are prescribed for differential diagnosis. First and foremost, osteoporosis must be distinguished from osteomalacia: hypocalcemia and increased hydroxyproline excretion are typical for osteoporosis, whereas alkaline phosphatase activity increases in osteomalacia.
Principles of treatment
Therapy must be long-term and comprehensive. Since an "ideal" drug does not exist, combination regimens are used. There are three main groups of medications:
- Antiresorptive drugs: inhibit bone destruction (bisphosphonates, estrogens, calcitonin, calcium supplements).
- Bone formation stimulators: enhance new tissue synthesis (fluoride derivatives, parathyroid hormone fragments, anabolic steroids).
- Dual-action drugs: affect both processes (active vitamin D metabolites, ossein-hydroxyapatite complex).
In addition to medications, patients are prescribed muscle corset strengthening exercises (physical therapy) to prevent falls, as well as spinal unloading when necessary.
Briefly: answers to topical questions
Which endocrine disorders most frequently lead to secondary osteoporosis?
Secondary osteoporosis is most commonly caused by the following endocrine disorders:
- Cushing's disease and syndrome (Cushing Disease / Syndrome) — accompanied by excess corticosteroids.
- Thyroid disorders (Thyroid Disease) — hyperthyroidism and thyrotoxicosis.
- Hyperparathyroidism — leads to enhanced bone tissue resorption.
- Hypogonadism — sex hormone deficiency.
- Insulin-dependent diabetes mellitus.
In which bones do typical osteoporotic fractures most frequently occur?
Typical osteoporotic fractures most frequently occur in the vertebrae, distal radius, and femur.
- Vertebral bodies — compression and wedge fractures (vertebral body compression fractures / wedge fractures).
- Proximal femur — femoral neck or intertrochanteric fractures (femoral neck or intertrochanteric regions).
- Distal radial metaphysis — Colles' fracture (Colles' fracture), as well as carpal bones.
Which bone turnover markers are tested in the blood to diagnose osteoporosis?
To diagnose osteoporosis, specific biochemical markers of bone remodeling are assessed in the blood. Markers of bone formation include:
- Bone-specific alkaline phosphatase;
- Osteocalcin;
- N-terminal propeptide of type 1 procollagen (P1NP).
The marker of bone resorption tested in the blood is:
- C-terminal telopeptide of type 1 collagen (CTX).
The most stable markers recommended for most patients are P1NP and CTX.
What are the specific radiological signs of spinal osteoporosis in late stages?
In late-stage spinal osteoporosis, radiographs reveal pronounced deformations of the vertebral bodies. Specific signs include:
- Wedge deformity (wedge fractures) — anterior collapse of the thoracic vertebral bodies, characteristic of the postmenopausal form and leading to posture deformity.
- 'Cod fish' vertebrae ('cod fish') — typical of glucocorticoid-induced osteoporosis.
Additionally, multiple compression fractures of the vertebrae are detected in late stages.
What are the contraindications for prescribing bisphosphonates?
Bisphosphonates are not recommended for female athletes with the female athlete triad for the treatment of low bone mineral density or osteoporosis, as their use in this group increases the risk of stress fractures. Bisphosphonates may be contraindicated in renal dysfunction; in such cases, RANK ligand inhibitors may be used.
What is the pathogenesis of bone loss in postmenopausal estrogen deficiency?
The pathogenesis of bone loss in postmenopausal estrogen deficiency involves accelerated resorption, predominantly of trabecular bone tissue.
- Accelerated bone loss — estrogen deficiency causes the rate of bone loss to exceed normal levels by a factor of 3 (amounting to 2–10% per year).
- Dynamics of the process — bone loss accelerates particularly during the first 5–10 years following menopause, manifesting clinically after 15–20 years.
To quickly assess a patient's height loss, measure their arm span from the tips of the third fingers. Normally, this value is equal to the person's initial height (before the onset of the disease).
Class and exam questions
What is the difference between osteopenia and osteoporosis?
Osteopenia is a moderate decrease in bone density (T-score from -1 to -2.5), often asymptomatic. Osteoporosis is a more pronounced loss of mass (T-score > -2.5), which significantly increases the risk of pathological fractures.
Why is a standard X-ray insufficient when osteoporosis is suspected?
Conventional radiography will show bone rarefaction only when the patient has already lost 20% to 40% of bone mass. Bone densitometry is required to detect early stages.
What does the onset of neurological symptoms indicate in a vertebral fracture?
In a typical osteoporotic vertebral fracture, spinal cord neurological deficit symptoms are extremely rare. Their appearance requires an urgent search for an oncological process (e.g., metastases).
What else to study on this topic
- Pathophysiology of Bone Remodeling
- Spondylarthrosis: Etiology and Clinical Features in Different Segments
- Differential Diagnosis of Secondary Osteoporosis
- Laboratory Markers of Calcium-Phosphorus Homeostasis
- Orthopedic Support and Physical Therapy in Spinal Deformities
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