Weight Loss and Cachexia

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Definitions & Differentiation - Weighing the Basics

  • Weight Loss (WL):
    • Clinically significant: >5% body weight loss in 6-12 months, involuntary.
  • Cachexia:
    • Multifactorial syndrome: ongoing muscle loss (± fat loss) from underlying illness.
    • Drivers: inflammation, ↑metabolism, ↑protein catabolism.
    • Common in: cancer, CHF, COPD, CKD, AIDS.
  • Differentiation:
    • Starvation: Mainly fat loss, ↓metabolic rate, responds to feeding.
    • Sarcopenia: Age-related ↓muscle mass, strength, & function.
    • Cachexia vs. Starvation: Cachexia involves inflammation & ↑Resting Energy Expenditure (REE); poor response to nutrition alone. Cachexia and Sarcopenia Causes and Effects

⭐ Cachexia is characterized by systemic inflammation, negative protein and energy balance, and involuntary loss of lean body mass, significantly impacting prognosis.

Etiology Spectrum - The Why Behind Wasting

  • Malignancy: Commonest in elderly. Pancreatic, lung, GI, hematologic.

    ⭐ Cancer cachexia: Driven by cytokines (TNF-α, IL-1, IL-6) & tumor factors (e.g., PIF).

  • Chronic Infections:
    • HIV/AIDS (wasting syndrome)
    • Tuberculosis (systemic effects)
    • Disseminated fungal/parasitic infections
  • Chronic Inflammatory (Non-infectious):
    • RA, SLE (systemic inflammation)
    • IBD (Crohn's, UC - malabsorption, inflammation)
  • Major Organ Failure:
    • Cardiac cachexia (CHF)
    • Renal cachexia (CKD Stage 4-5)
    • Hepatic cachexia (cirrhosis)
    • Pulmonary cachexia (COPD)
  • Endocrine:
    • Hyperthyroidism (↑BMR)
    • Uncontrolled DM (catabolism)
    • Addison's disease (anorexia)
  • GI (Non-malignant):
    • Malabsorption (celiac, sprue)
    • Chronic pancreatitis (exocrine insufficiency)
    • Gastroparesis, esophageal strictures
  • Neuropsychiatric:
    • Depression, Anorexia nervosa
    • Advanced dementia (↓intake, dysphagia)
  • Medications: Chemotherapy, stimulants, SSRIs (some), digoxin toxicity.
  • Other: Poverty, substance abuse, elder neglect, dental issues. Mechanisms of Cachexia

Pathophysiology Unveiled - Cytokine Chaos

  • Pro-inflammatory Cytokines: Central to cachexia. Key players: TNF-α, IL-1, IL-6, IFN-γ.
    • Secreted by tumor and/or host immune cells (macrophages, T-cells).
  • Mechanisms of Wasting:
    • ↑ Muscle Protein Breakdown: Primarily via Ubiquitin-Proteasome System (UPS) activation; autophagy also involved.
    • ↓ Protein Synthesis: Due to impaired anabolic signaling (e.g., Akt/mTOR pathway inhibition).
    • ↑ Lipolysis: Adipose tissue breakdown, releasing fatty acids; mediated by factors like ZAG.
    • Anorexia: Cytokines act on hypothalamus (e.g., NPY/AgRP, POMC/CART neurons), reducing appetite.
    • ↑ Resting Energy Expenditure (REE): Contributing to negative energy balance.
  • Specific Cachectic Factors:
    • Proteolysis-Inducing Factor (PIF): Induces muscle protein degradation.
    • Lipid Mobilizing Factor (LMF): Stimulates lipolysis.
  • Hormonal Imbalance:
    • ↓ Anabolic hormones (e.g., Testosterone, IGF-1).
    • ↑ Catabolic hormones (e.g., Cortisol, Glucagon).

⭐ TNF-α (also known as Cachectin) is a pivotal cytokine that directly promotes muscle catabolism (especially via NF-κB pathway) and suppresses appetite, significantly contributing to the cachectic state.

Pathophysiology of Cachexia

Evaluation & Management - Charting the Course

  • Core Principle: Address the root cause.
  • Nutritional Support:
    • Goal: High-calorie, high-protein intake.
    • Methods: Diet modification, Oral Nutritional Supplements (ONS), enteral/parenteral feeding.
  • Pharmacotherapy (Cachexia):
    • Appetite stimulants: Megestrol acetate, mirtazapine.
    • Corticosteroids (short-term).
  • Supportive Care: Symptom control, psychosocial support.
  • Palliative approach: If advanced/irreversible disease.

⭐ In elderly patients with unexplained weight loss, malignancy and non-malignant GI diseases are the most common etiologies.

High‑Yield Points - ⚡ Biggest Takeaways

  • Significant involuntary weight loss is defined as >5% of usual body weight over 6-12 months.
  • Cachexia is weight loss coupled with systemic inflammation (e.g., in cancer, CHF, COPD, AIDS), mediated by cytokines like TNF-α, IL-1, IL-6.
  • Differentiate cachexia from starvation (simple nutrient deprivation, no marked inflammation) and sarcopenia (age-related muscle loss).
  • Initial workup includes a thorough history, physical examination, and basic laboratory tests (CBC, ESR, CRP, TSH, FOBT).
  • Prioritize ruling out occult malignancy, especially in older adults; management focuses on treating the underlying cause and providing nutritional support.

Practice Questions: Weight Loss and Cachexia

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