Q5 LONG ANSWER 10M ★ High-yield

Define Metastatic Bone Disease. Describe its clinical features, investigations, management and prognosis.

General Surgery · Final Professional

Definition & Importance

Metastatic (secondary) bone disease is by far the commonest malignant tumour of bone in adults — far more frequent than all primary bone sarcomas combined. Any bone lesion in a patient over 40 should be considered metastatic until proven otherwise. The primary tumours that most often spread to bone are remembered as the ‘famous five’: breast, prostate, lung, kidney (renal) and thyroid.

	Osteolytic	Osteoblastic (sclerotic)
Typical primaries	Kidney, thyroid, lung, breast	Prostate (breast can be mixed)
X-ray	Bone destruction/lucency	Increased bone density
Fracture risk	High	Lower

Clinical Features

Bone pain (progressive, often worse at night), a pathological fracture (sometimes the presenting event), and features of hypercalcaemia (thirst, polyuria, confusion, constipation). Spinal deposits may cause cord or cauda equina compression. There may be symptoms of the primary tumour, or the primary may be occult.

DANGER / REMEMBER

A pathological fracture or spinal metastasis with neurological signs is an oncological emergency. New back pain with neurology in a cancer patient is metastatic spinal cord compression until proven otherwise — arrange urgent MRI and treatment (steroids, radiotherapy or surgery).

Investigations

Radiographs of the symptomatic site (lytic or sclerotic deposits); a bone scan surveys the skeleton (though purely lytic myeloma may be missed). Blood tests: calcium, alkaline phosphatase, renal and liver function, PSA (prostate), and a myeloma screen where relevant. The primary is sought with CT chest/abdomen/pelvis, mammography, PSA, thyroid imaging, etc.; biopsy confirms metastasis and identifies the tissue of origin when the primary is unknown.

Management

Treatment is usually palliative and multidisciplinary, aimed at pain relief, preserving function and preventing/treating fractures. Modalities include analgesia, radiotherapy (excellent for localised bone pain and after fixation), bisphosphonates or denosumab (to reduce skeletal events and treat hypercalcaemia), and systemic therapy for the primary (hormonal, chemotherapy, targeted agents). Surgical stabilisation (internal fixation or prosthetic replacement) is indicated for an actual or impending pathological fracture (predicted by the Mirels score) and for spinal instability/cord compression.

CLINICAL PEARL

For a suspected impending fracture of a long-bone metastasis, the Mirels score (site, pain, lytic vs blastic, and size of the lesion) guides prophylactic fixation — fixing before the bone breaks is far better than after.

Prognosis

Prognosis depends on the primary tumour and the overall disease burden. Breast, prostate and thyroid bone metastases may be compatible with prolonged survival with modern systemic therapy, whereas lung primaries generally carry a poorer outlook; the goal throughout is quality of life and function.

Routes of Spread & Distribution

Bone metastases usually spread haematogenously, favouring the red-marrow-rich axial skeleton — the spine, pelvis, ribs, skull and proximal femur/humerus — whereas deposits distal to the elbow and knee are uncommon (and, when present, are classically from a bronchial or renal primary). The vertebral venous plexus of Batson is an important valveless route that helps explain the predilection of prostate and other pelvic tumours for the spine.

DANGER / REMEMBER

Because a solitary bony metastasis can occasionally be the first sign of an unknown primary, and because a solitary destructive lesion in an older adult could still be a primary sarcoma or myeloma, biopsy is advisable before fixing a presumed metastasis when the diagnosis is not already secure — confirming the tissue of origin also guides systemic treatment.

Commonest bone malignancy overall — far exceeds primary tumours.

KEY POINT

Key points TO remember

Commonest bone malignancy in adults; any bony lesion >40 y is metastatic until proven otherwise.
Primaries: breast, prostate, lung, kidney, thyroid. Prostate is classically osteoblastic; kidney/thyroid lytic.
Bone pain, pathological fracture, hypercalcaemia, cord compression.
Bone scan surveys skeleton (myeloma may be missed); seek the primary; biopsy if unknown.
Palliative MDT care: analgesia, radiotherapy, bisphosphonates/denosumab; fix actual/impending fractures (Mirels).

EXAM TIP

Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.

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