29 November 2021, Monday

What Investigations Can Be Done to Detect/Diagnose Bone Metastasis?

There are several investigations which can contribute in the detection/diagnosis of Bone Metastases. Some of the important ones are as follows:

X-ray:

Despite the advances in medical imaging technology‚ standard plain X-ray with normal magnification remains one of the most common and useful investigations to detect Bone Metastasis. However‚ X-ray is generally best suited for imaging symptomatic areas only.

Bone scan:

Bone scan is generally regarded as the most cost-effective whole-body screening test for the detection of Bone Metastases. This is a nuclear imaging investigation which is highly sensitive and can detect Bone Metastases earlier than X-ray. In a single study‚ the entire skeletal system of the patient can be investigated for Bone Metastasis.

However‚ it is not a very specific investigation. This means that‚ although bone scan is very sensitive and picks up even small problems in the bones‚ it cannot help in identifying the cause of that problem. Bone scan also highlights other lesions like arthritis‚ healing fracture‚ benign bone tumor‚ infection‚ etc. It is‚ therefore‚ necessary to interpret the bone scan findings carefully.

Computed Tomography (CT) scan:

CT-scan uses X-rays to provide cross-sectional images of the bone, which may reveal details missed on a conventional X-ray. It is particularly useful in targeting biopsy needles to‚ small and deep‚ difficult to access‚ suspected Bone Metastasis; located‚ for example‚ in the vertebrae.

Magnetic Resonance Imaging (MRI):

MRI scans use radio waves and strong magnets instead of X-rays to provide pictures of bones and tissues. It is a highly sensitive investigation and can detect small and deep Bone Metastases early.

Positron Emission Tomography (PET):

PET scan is a recent nuclear imaging investigation‚ useful in the staging of patients with cancer. The advantage of PET scan in the work-up for metastasis is that it can detect metastasis in most of the tissues of the body including the bone; unlike bone scan‚ which is specifically designed for the skeletal system only.

In PET scan, radio-labelled glucose synthetic glucose molecules‚ with a positron emitting radioactive atomincorporated into its structure) is injected into the body‚ which is detected by the PET scanner machine. PET can detect accurately the various metastases in the body if there is any. However‚ in the detection of Bone Metastasis‚ the excellent sensitivity of a bone scan generally limits the need for a PET scan. PET scan is an expensive investigation.

Blood investigations:

Bone Metastasis can cause alterations in the blood levels of certain substances. It can cause a rise in calcium and alkaline phosphatase levels. However‚ the blood level of these substances can also rise due to other causes. So‚ one must be cautious in interpreting the findings. Another useful investigation in the work-up for skeletal metastasis is the study of ‘Tumor Markers’ levels.

‘Tumor Markers’ are certain substances‚ which may be/are‚ found in higher quantities in blood‚ body tissue‚ body fluids‚ urine‚ etc.‚ in the presence of certain cancers‚ e.g. PSA in prostate cancer‚ etc. Elevated ‘Tumor Markers’levels, in the presence of unexplained bone lesions‚ should raise the suspicion of Bone Metastasis due to the cancer represented by the Tumor Marker.

Except in some cancers, ‘Tumor Markers’‚ although helpful in some ways, are not very reliable and the interpretation of their values should be done in the light of other findings and evidence; a job best left to your treating doctor.