Hyaline Degeneration

Introduction

Hyalisation of muscle fibrils of skeletal, intercostal, diaphragmatic and cardiac muscles. Histologically there is Zenker degeneration and occasionally also dystrophic calcification.

Grossly the condition is seen as grey/yellow streaks on the innermost part of the myocardium.

The condition is associated with Vitamin/Selenium deficiency. Also known as nutritional myopathy or White muscle disease. The myocardium of the left ventricle is most affected as it has the largest metabolic demand and so the largest production of anti-oxidants and the greatest need for Vitamin E/Selenium. This manifests clinically as left sided heart failure with clinical signs:

• Pulmonary oedema.

Also:

• Acute ataxia and collapse with the skeletal muscles affected.

Also associated with a diet over-rich in unsaturated fatty acids seen in pigs (Vitamin E/Selenium unavailable as used up by the unsaturated fats).

• The term "hyaline degeneration" is applied to several types of degeneration or infiltration.
  • "Hyaline" is a descriptive term meaning "glassy".
    • Used in pathology when structureless material appears in section, and stains red with eosin
      • Describes a variety of conditions in which structureless materials are present.
• Is applied to both extra- and intra-cellular degenerations/ infiltrations. ** Extracellular
  • • Protein hyaline casts in the renal tubules.
      • From excessive protein passing through glomerulus.
      • When fresh urine is examined under the microscope, casts may be seen as elongated glassy tubes.
    • Hyaline membranes
      • Proteinaceous effusions into pulmonary alveoli
      • Prevent gaseous exchange. ** Intracellular
    • Hyaline degeneration of skeletal muscle.
      • In vitamin E/ selenium deficiency.
• There are two forms of hyaline degeneration that deserve their own mention.
  • Fibrinoid degeneration.
  • Amyloid infiltration.

Fibrinoid Degeneration

• Fibrinoid degeneration features a material which is fibrin-like.
• Is essentially a focal death of cells in the walls of small blood vessels (usually arterioles).
  • Parts of the vessel wall become replaced by a granular material.
    • Pinkish-red (i.e. eosin-staining).
    • Has some of the appearance and staining properties of fibrin.
    • Consists partly of degenerated muscle and elastic fibres, and partly of an increased amount of protein ground substance around the degenerated fibres.
    • Looks like a red smudge in the vessel wall when viewed histologically.
• The presence of the fibrin-like material may suggest
  • A local hypersensitivity reaction
  • Hypertension

Amyloidosis

• Also known as amyloid infiltration
• Deposition of a proteinaceous hyaline substance in extracellular sites.
  • Sites of deposition vary with species.
• The kidney is a common site of deposition.
  • Amyloid is deposited under the capillary endothelium and progressively increases in volume.
• There are various categories of amyloid.
  • Is essentially an abnormal protein produced in the body
  • In most cases, it is produced in response to sustained antigenic stimulation caused by a chronic suppurative process.
    • E.g. a foot abscess, mastitis.
• Amyloid is a relatively inert substance.
  • When it accumulates, it is not easily removed.

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