Blindness as the presenting sign of osteopetrosis in a child.

A 1-year-old female child presented with complaints of defective vision since birth. On examination, the child showed wandering nystagmoid movements. She did not either follow or fixate on torchlight examination. Fundus examination revealed bilateral optic disc pallor. Magnetic resonance imaging of the brain and orbit showed diffuse thickening of the calvarium, widened diploic space, and extensive sclerosis [Figure 1a and d]. Significant narrowing of the optic canals with thinning of the optic nerves and optic chiasm were noted [Figure 1b and d]. An X-ray of the pelvis confirmed osteopetrosis with dense sclerosis and thickening of the pelvic bones and both femurs [Figure 1c]. The characteristic parallel bands of dense bone giving the appearance of “bone within bone” and club-shaped flaring of the metaphyses of the femur with cortical thinning leading to the “Erlenmeyer flask” deformity were seen.

Figure 1

(a) T1-weighted axial magnetic resonance imaging scan showing diffuse sclerosis seen as hypointense calvarial and skull base thickening with widened diploic space (b) T2-weighted axial magnetic resonance imaging (FIESTA sequence) showing narrowing of the optic nerve canals with optic nerve thinning (arrows). (c) Radiograph of pelvis and femur showing characteristic “bone within bone” appearance and the “Erlenmeyer flask” deformity of the femur. (d) T2-weighted coronal magnetic resonance imaging scan showing narrowing of optic nerve canals (yellow arrows)

The child was referred to a pediatric specialty hospital for further evaluation and management but was lost to follow-up.

Osteopetrosis patients seldom present to the ophthalmologists with visual loss as the presenting symptom. Though rare, pediatric ophthalmologists and neuro-ophthalmologists should be aware of this condition, as a timely referral for hematopoietic stem cell transplantation (HSCT) may reverse the visual loss.[1]

Discussion

Osteopetrosis is the generic name given to a group of rare single-gene disorders characterized by sclerosis of the skeletal system.[2] It is due to a decreased or a complete lack of osteoclast function, and therefore, impairment of bone resorption. It presents in varying degrees of severity and modes of inheritance. Infantile recessive (malignant) osteopetrosis is the most severe form and is usually lethal in childhood without treatment. These patients usually present with pathological fractures due to increased bone fragility or failure to thrive.[3] The most common ophthalmic complication is compressive optic nerve neuropathy leading to atrophy, and subsequently blindness, due to the narrowing of the surrounding optic foramen. Other causes of diminution of vision include progressive chorioretinal degeneration and obstructive hydrocephalus.[14] Proptosis may result from shallow orbits caused by the thickening of the orbital bones. Pyknodysostosis, an extremely rare autosomal recessive disorder, should be considered as a differential for sclerotic bone in a child.[5]

Optimal care of patients with osteopetrosis requires the involvement of a multidisciplinary team that depending on the severity and clinical comorbidities. Bone marrow failure and age <1 year at diagnosis are primary indications for HSCT. Genetic testing may reveal specific mutations that favor or preclude (e.g., OSTM1 or RANKL mutations) bone marrow transplantation.[4] Management options for preventing vision loss include optic nerve sheath fenestration, optic canal decompression, and ventriculoperitoneal shunt surgeries.[1]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.