Makindo Medical Notes

Related Subjects: |Osteoporosis |Osteogenesis Imperfecta |Osteopetrosis

🦴 About

• Osteopetrosis (aka Marble Bone Disease or Albers-Schönberg disease) is a rare inherited disorder of defective bone resorption due to abnormal osteoclast function.
• The terms “benign” and “malignant” do not imply cancer but describe disease severity.
• Hallmark: Bones appear dense on X-ray but are paradoxically brittle.

🔎 Types

• 1. Autosomal Recessive – “Malignant” Form:
  • Onset in infancy/childhood 👶.
  • Associated with renal tubular acidosis and neuronal storage disease.
  • Cranial nerve compression ➝ visual loss, hearing loss, facial palsy.
  • Bone marrow failure ➝ anaemia, thrombocytopenia, hepatosplenomegaly (extramedullary haematopoiesis).
  • Other features: nasal obstruction, recurrent infections, short stature, bone deformity.
• 2. Autosomal Dominant – “Benign” Form:
  • Later presentation in adolescence/adulthood 🧑.
  • Fragility fractures despite dense bones.
  • Prone to osteoarthritis & cranial nerve compression.
  • Tends to have a milder, more chronic course.

⚠️ Clinical & Pathophysiology

• Defective osteoclast acidification (e.g. Carbonic anhydrase II deficiency) or chloride channel mutations impair bone resorption.
• Classic features:
  • 💥 Fragility fractures.
  • 📈 Increased bone density on X-ray (“stone bone”).
  • 📉 Bone marrow suppression ➝ pancytopenia & extramedullary haematopoiesis.
  • Raised acid phosphatase & bone-specific CK-BB.
  • Neurological sequelae from cranial nerve entrapment.

🛠️ Management

• Supportive: Calcium restriction in diet, prompt treatment of infections.
• Pharmacological: Corticosteroids (e.g. prednisolone) may improve marrow space.
• Complication Care: Hyperbaric O₂ for osteomyelitis 💉; surgical decompression for cranial nerve entrapment.
• Definitive: 💉 Bone marrow transplant (BMT) – provides normal osteoclasts ➝ potential cure in severe AR cases.

📌 Key Exam Pearls

• Radiology buzzword: “Bone within bone” or “Erlenmeyer flask deformity” of femur.
• AR form ➝ fatal in childhood without BMT (due to marrow failure & infections).
• AD form ➝ milder, fractures + cranial nerve palsies but usually compatible with long survival.
• Differentiate from Paget’s disease (↑ bone turnover) & osteogenesis imperfecta (fragile bones but low density).

Cases — Osteopetrosis

• Case 1 — Infantile malignant form 👶: A 9-month-old boy presents with failure to thrive, recurrent chest infections, and pallor. Exam: hepatosplenomegaly and cranial nerve palsies. Bloods: pancytopenia. Skeletal survey: diffuse sclerosis and “bone-in-bone” appearance. Diagnosis: autosomal recessive infantile osteopetrosis. Prognosis poor without haematopoietic stem cell transplant.
• Case 2 — Adult benign form 🧍‍♂️: A 34-year-old man presents with recurrent fractures after minor trauma and progressive hip pain. Radiographs: increased bone density with thickened cortices. No cytopenias. Diagnosis: autosomal dominant adult osteopetrosis. Managed conservatively with orthopaedic support.
• Case 3 — Intermediate form 🧒: A 12-year-old girl reports progressive visual and hearing loss with frequent headaches. Exam: optic atrophy and conductive deafness from cranial nerve compression. CT skull: thickened, sclerotic bone narrowing foramina. Diagnosis: intermediate osteopetrosis with cranial nerve entrapment. Managed symptomatically; surgical decompression considered.

Teaching Point 🩺: Osteopetrosis is a rare inherited disorder of defective osteoclast function leading to excessively dense but brittle bone. Clinical spectrum ranges from fatal infantile disease to mild adult forms. Complications include fractures, marrow failure, cranial nerve palsies, and recurrent infections.