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A single slice of a CT scan at the third lumbar vertebra measures how much skeletal muscle a person has, and the scan has usually already been taken for staging. Low muscle predicts worse outcomes and more chemotherapy toxicity, including in people whose weight looks normal or high.
Weight and body mass index are poor measures here, because treatment changes the composition of a body more than its mass. Two people at the same weight can differ by many kilograms of muscle, and the one with less is at the greater risk.
The method that made this practical. Cross-sectional area of skeletal muscle on a single axial CT image at the third lumbar vertebra correlates closely with whole-body muscle mass and is measurable on scans already taken for staging and response assessment. Prado and colleagues analysed a population-based cohort of 2,115 patients with respiratory or gastrointestinal tract tumours in northern Alberta. Of those, 325 (15 per cent) had a body mass index of 30 or more; 250 of them had analysable images. Sex-specific cut-offs for low muscle were derived by optimum stratification, and 38 of 250, 15 per cent, fell below them. Sarcopenic obesity was associated with worse functional status and was "an independent predictor of survival (hazard ratio [HR] 4.2 [95% CI 2.4-7.2])". The reason that paper matters is in its own framing: these were obese patients, and muscle depletion inside obesity is invisible to the scales.
The other methods. Dual-energy X-ray absorptiometry measures lean mass, fat mass and bone density in one scan and is the reference for bone; it is the scan used to follow treatment-induced bone loss. Bioelectrical impedance analysis is cheap and portable but is affected by hydration, which is a real problem in people having infusions, vomiting or developing oedema. Ultrasound of the quadriceps is emerging for bedside use.
Why it belongs on a recovery page. Muscle lost during treatment is the thing that makes stairs hard afterwards, and it is the thing resistance training rebuilds. Body composition is how you tell whether it actually came back, and it distinguishes recoverable disuse atrophy from cancer cachexia, which by its own consensus definition cannot be fully reversed by nutritional support while the cancer is active.
What it misses. Muscle cross-sectional area is quantity, not quality or strength; a muscle can be infiltrated with fat and perform poorly at normal area, and radiodensity is a partial correction for that. The cut-offs are population-specific and the ones in widest use were derived in North American cohorts, so they transfer imperfectly to Asian and African populations. Software and reader variation between centres is a known source of disagreement. And a CT slice is only available if someone is still having CT scans, which after treatment ends is often no longer the case.
Skeletal muscle and adipose tissue have distinct Hounsfield unit ranges on CT, so a single axial slice at the third lumbar vertebra can be segmented into tissue compartments whose cross-sectional areas scale predictably to whole-body mass, giving a quantitative body composition measurement from an image acquired for another purpose.
Query for this technology: (TITLE:"Measuring muscle and fat on scans the patient already had" OR ABSTRACT:"Measuring muscle and fat on scans the patient already had") AND (cancer OR tumor OR tumour OR oncology OR carcinoma OR lymphoma OR leukemia OR leukaemia OR myeloma OR sarcoma OR melanoma OR glioma). Results are unfiltered search hits about Measuring muscle and fat on scans the patient already had, not a curated reading list.
Shares Walking, gripping and standing up: the tests that take five minutes, Survivorship and late effects are neglected, Colorectal cancer, Non-small-cell lung cancer and the tags rejuvenation, survivorship, measurement, objective.
Shares Cardiopulmonary exercise testing: the hardest number in recovery, Walking, gripping and standing up: the tests that take five minutes, Sarcopenia, Survivorship and late effects are neglected and the tags rejuvenation, survivorship, measurement.
Shares Muscle and strength after treatment: sarcopenia, cachexia and what rebuilds, Walking, gripping and standing up: the tests that take five minutes, Sarcopenia, Survivorship and late effects are neglected and the tags rejuvenation, survivorship, measurement.
Shares Cardiopulmonary exercise testing: the hardest number in recovery, Muscle and strength after treatment: sarcopenia, cachexia and what rebuilds, Resistance training and protein for cachexia and sarcopenia, Walking, gripping and standing up: the tests that take five minutes and the tags rejuvenation, survivorship.
Shares Walking, gripping and standing up: the tests that take five minutes, Survivorship and late effects are neglected, Colorectal cancer, Non-small-cell lung cancer and the tags rejuvenation, survivorship, measurement.
Shares Survivorship and late effects are neglected, Colorectal cancer, Non-small-cell lung cancer and the tags rejuvenation, survivorship, measurement.
Shares Survivorship and late effects are neglected, Colorectal cancer, Non-small-cell lung cancer and the tags rejuvenation, survivorship, measurement.
Shares Sarcopenia, Nutrition support and cachexia management, Survivorship and late effects are neglected, Oesophageal cancer and the tags rejuvenation, survivorship.