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Paget’s disease of bone


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of pharmacology and clinical reasoning topics. Try it free today. Paget’s disease of bone is a disorder in
which there’s a lot of bone remodeling that happens in some regions of the bone. Typically there’s excessive bone resorption
followed by excessive bone growth, and it leads to skeletal deformities and potential
fractures. Normally, bones undergo a continuous process
of bone remodeling. Old brittle bone tissue gets reabsorbed by
multinucleated bone cells called osteoclasts, which have 5 to 20 nuclei per cell. The resorbed bone tissue gets replaced by
a new one made by another type of bone cell called an osteoblast. At the cellular level, the process begins
when osteoblasts release receptor activator of nuclear factor κβ ligand, or RANKL for
short, which is a substance that binds to RANK receptors on the surface of osteoclast. When RANKL binds to the RANK receptor, it
activates the osteoclasts, and they start secreting lysosomal enzymes like collagenase
as well as hydrochloric acid. Together they digest the collagen protein
and dissolve the minerals that make up the bone matrix. Once there’s been sufficient bone demineralization,
the osteoblasts secrete another substance called Osteoprotegerin, or OPG for short,
which binds RANKL and prevents it from activating the RANK receptors. This causes the osteoclasts to stop demineralizing
the bones. Once that happens, the osteoblasts start secreting
a substance called osteoid seam, which is mainly made up of collagen and acts like a
scaffold upon which calcium and phosphate can get deposited. And that’s how new bone begins to get formed
again. The exact cause of Paget disease of bone is
unclear, but it can get triggered by infections like the measles virus, and is linked to genetic
mutations like the SQSTM1 mutation, which encodes a protein involved in regulating osteoclasts. When Paget disease of bone occurs, it can
affect a single bone or the whole skeletal system. Most often, it involves the skull, lumbar
vertebrae, the pelvis, and the femur. Now, there are three main phases to the disease. Phase one is the lytic phase, and that’s
where osteoclasts, which have up to 100 nuclei, start to aggressively demineralize the bone
up to 20 times more than normal. Phase two is the mixed phase, and that’s
where the lytic phase occurs alongside the blastic phase. In the blastic phase, there’s a rapid but
relatively disorganized proliferation of new bone tissue by an unusually large number of
osteoblasts. The result is that collagen fibers are deposited
in a haphazard way. Phase three is the sclerotic phase, and that’s
where new bone formation exceeds bone resorption, and the final result is bone that’s structurally
disorganized and therefore weaker than normal healthy bone. Eventually, the osteoblastic activity also
slows down, and there’s a dormant state in the disease, called the “burned- out
state”. Early on Paget disease of bone doesn’t typically
cause symptoms, but over time, the misshapen bones can impinge on nerves and cause pain. In addition, if the skull is involved, the
overgrowth of bones can make a person have a lion- like face, which is called leontiasis. The bony overgrowth can also narrow the auditory
foramen and impingement on the auditory nerve, leading to hearing loss. If there’s bony overgrowth that impinges
on the optic nerve as it passes through the optic canal – that can lead to vision loss. Sometimes the accelerated bony growth can
lead to genetic mutations that cause a bone cancer called osteosarcoma. When that happens it’s referred to as Paget
sarcoma. Other bony deformities from Paget disease
of bone include kyphosis – which is an excessive curvature of the spine making a person face
down to the ground, lower limb muscle weakness – from misshapen vertebrae compressing the
spinal cord, and pelvic asymmetry. It can even lead to bowlegs if the femurs
get too weak to support a person’s weight and begin to bend over time. If the parts of the bone that are involved
in a joint are involved, it can result in arthritis or joint inflammation. The diagnosis of Paget disease of bone is
usually done by checking for elevated levels of alkaline phosphatase. In addition, an X-ray might show lytic lesions
during the lytic phase of the disease, or thickened bone cortices in advanced cases. Finally, a bone biopsy is usually done to
exclude malignancies which can mimic some of the findings of Paget disease of bone. Treatment of Paget disease of bone includes
pain relievers as well as antiresorptive medications like bisphosphonates which slow down the bone
lysis. In addition, surgery can help correct bone
deformities, decompress an impinged nerve, and reduce associated fractures. Alright, as a quick recap, … in Paget disease
of bone there’s an excessive amount of bone resorption and haphazard bone growth. There’s a lytic phase, a mixed phase with
both a lytic and blastic component, and a sclerotic phase which results in weak bone. Paget disease of bone is usually asymptomatic,
but can result in weak, misshapen bones that cause fractures and lead to nerve compression.

25 thoughts on “Paget’s disease of bone

  1. bone and jiont disorder is when acute inflammatory bone marrow its structure to secondary infection

  2. Thank u so much !
    But i have a question : when we decide that the level of alkaline phosphatase is sufficient to diagnose the disease ?

  3. U guys should add at least these English subs to the videos in the Ósmosis platform. It's a really good resource for a Medicine student.

  4. I hate my medical school so much. But your adorable animations make me fall back in love with medicine again.

  5. Is there any ayervedic treatment for skull paget in india?? One of my family member female is taking very strong steriods for skull paget as recommended by doctor. She is in very much pain because of the issue & high doses of medicine.
    Please help us out if there is some ayervedic treatment which can help her out. She has been taking medicine since last 20-25years

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