Paediatrics: Osteopetrosis

Osteopetrosis

Also known as marble bone disease or Albers–Schönberg disease. This is a rare chromosomal condition defined by failure of osteoclastic bone resorption and hence failure of remodelling.

Classification

•   Malignant/infantile type: AR. Severe skeletal deformity presenting at birth or shortly after. Poor prognosis. Bone marrow transplantation may help in some cases.

•   Benign type: AD. Later childhood/adulthood benign presentation. Prone to frequent fractures.

Clinical features

•   Face: macrocephaly, hydrocephalus, ‘abnormal eyes’ (optic atrophy, partial oculomotor nerve paralysis), compression of other cranial nerves resulting in deafness, facial nerve palsy.

•   Teeth: late eruption; early caries, osteomyelitis, and necrosis of mandible.

•   Limbs: generalized osteosclerosis, fragile bones (due to failure to form lamellated bone in stress areas) with fractures that are difficult to fix and prone to delayed union, dwarfism.

•   Haematological: encroached marrow cavities leading to anaemia, pancytopenia, spontaneous bleeding/bruises. Spleen (extra medullary haemopoiesis leading to hepatosplenomegaly).

•   Kidneys: causes distal renal tubular acidosis (type 1 RTA).

Investigations

•   Blood: pancytopenia and leucoerythroblastic picture (increased primitive cells in blood film). Dry bone marrow tap.

•   X-rays: dense ‘marble’ bone (generalized increased density with loss of normal trabecular pattern).

•   Skull: underdeveloped mastoid air cells and paranasal sinuses.

•   Long bones: widened ends (‘Erlenmeyer flask’ proximal humerus/distal femur).

•   phalanges—dense transverse band in metaphysis close to epiphyseal line, condensed bone proximal and distal ends of phalanges;

•   metacarpals—‘bone within a bone’ appearance—sclerotic cortex separated from central bone by area of normal calcification;

•   vertebral bones—‘sandwich/rugger jersey’ appearance—relative sclerotic upper and lower plates;

•   bone scan—increased uptake in epiphyseal ends of long bones; normal elsewhere.

Treatment

Depends on severity of disease and is mainly supportive. Medical therapy includes glucocorticoids. Bone marrow transplant may help. Treatment of fractures is difficult due to dense bone quality.

Prognosis 

Malignant  type—usually  terminal  within  first  10yrs  of  life.

Benign form—lifespan unaffected.