Osteopetrosis, also known as marble bone disease, Albers-Schönberg disease, or primary fragile osteosclerosis, is sometimes referred to as chalk bone. It is a rare systemic skeletal disorder characterized by extreme bone density and loss of normal bone structure, resembling marble. However, the bones become brittle and prone to fractures. The condition may also be accompanied by anemia, optic atrophy, and deafness. As a rare disease, it is often discovered incidentally through X-ray examinations following fractures or other complications. Males are slightly more affected than females. Generally, it is believed that most patients develop the condition before symptoms appear. Clinically, it is classified into malignant (infantile) and benign (adult) types. The former often results in stillbirth or death shortly after birth due to anemia, with a poor prognosis.

bubble_chart Etiology

Unknown. It may be a congenital developmental abnormality, primarily caused by impaired bone resorption during bone development, leading to excessive calcium salt deposition and resulting in osteosclerosis. There is a clear hereditary and familial history, with both autosomal dominant and recessive inheritance patterns.

bubble_chart Pathological Changes

Both intramembranous and endochondral ossification can be affected. The bone becomes dense and thickened, completely losing its trabecular structure. The most pronounced changes are typically observed in the metaphyses of bones with the most vigorous growth, namely the distal ends of the femur and radius, and the proximal ends of the humerus and tibia. On cross-section, the cortex and medullary cavity are indistinguishable, with both ends expanding into a club-like shape, indicating impaired bone modeling. Microscopically, highly calcified cartilage fails to resorb and ossify, while calcified new bone also cannot remodel into mature lamellar bone. The bone cortex shows poor differentiation and disorganized arrangement, with deformed and incomplete Haversian systems. Underdeveloped osteoclasts are the direct cause of impaired bone resorption, and the medullary cavity is filled with fibrous tissue containing minimal sclerotic capillaries. Regarding bone hardness, some describe it as hard as stone, capable of breaking metal surgical instruments and unsuitable for bone traction. However, others have found diseased bone easier to penetrate than normal bone, producing no sound when cut—like carving chalk—hence the suggestion to name it "osteopsathyrosis" or "chalk bone." Despite its density, the bone is highly brittle and prone to fractures.

It can be asymptomatic. Some patients have a petite stature, delayed development, are prone to fractures, and experience slow healing. However, malunion does not occur, which differs from osteogenesis imperfecta. The skull becomes sclerotic, leading to hydrocephalus and compression of cranial nerves, resulting in eye atrophy, deviation of the mouth, hearing loss, and other symptoms. The paranasal sinus cavities decrease in size, becoming obstructed and poorly drained, leading to sinusitis. Anemia occurs in about 30% of cases and can be fatal in severe cases, often accompanied by compensatory enlargement of the spleen, liver, and lymph nodes. Dental caries are common, leading to mandibular osteomyelitis. Some patients may exhibit pigeon breast and beaded ribs.

X-ray findings: The hallmark is dense, thickened bones that lose their original structure, making it impossible to distinguish between the cortex and medullary cavity. The ends of the bones become enlarged and club-shaped. Some affected infants already exhibit these features in the uterus. Most bones in the body can be involved, but the mandible is rarely affected. Since the process of bone sclerosis can slow or pause, transverse striations of varying depths may be observed on the bones. The epiphyses are also dense and may sometimes appear concentric. The upper and lower ends of the vertebral bodies are dense, but the middle portion has a band of normal bone density, often described as a "sandwich vertebra." The skull also becomes sclerotic, with the disappearance of air sinuses, a shallow pituitary fossa, hyperplasia of the dorsum sellae, narrowing of the cranial fossae, and shrinkage of the cranial foramina.

bubble_chart Diagnosis

Due to the distinctive X-ray findings, diagnosis is not difficult. It should be differentiated from heavy metal poisoning, fluoride and vitamin D toxicity, hypothyroidism, and congenital syphilis.

bubble_chart Treatment Measures

There is no specific treatment. Some use 51Cr-labeled red blood cells. If shortened red blood cell lifespan and increased destruction of red blood cells in the spleen are observed, a splenectomy should be performed. The therapy involving low calcium intake and 7.5–10 g/d of phosphate cellulose is quite controversial. Prednisone is sometimes used to control anemia but has adverse effects on bone growth. Protect the teeth to avoid refractory mandibular osteomyelitis. If complicated by a fracture, the treatment principles are the same as for normal individuals. Occasionally, nerve decompression and ventricular drainage may be required.

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In the malignant type, most cases result in stillbirth or death shortly after birth, with the causes being infection and anemia; in the benign type, the prognosis is good, but it varies depending on the degree of anemia and its compensatory status.