Background: Osteopetrosis is a rare hereditary disorder of osteoclast dysfunction characterised by abnormally dense yet brittle bones. Spinal involvement is uncommon, and multilevel spondylolysis has been reported only in a handful of cases, usually in severe infantile or intermediate forms. Remodelling or healing of pars defects in osteopetrotic bone is exceptionally rare due to impaired bone resorption.

Case Presentation: We report a 54-year-old male with genetically and radiologically confirmed osteopetrosis who presented with low back pain radiating to the left lower limb for three months. Lumbar spine radiographs revealed multilevel pars interarticularis defects involving L3–L5, with focal sclerosis and partial remodelling of the pars at L4. This finding is notable, as bone healing is typically limited in osteopetrosis. The localised sclerosis and facet hypertrophy at L4 were associated with foraminal narrowing and L5 nerve root irritation. The patient was managed conservatively with a 10-day course of low-dose corticosteroid, pregabalin, and a muscle relaxant, achieving complete symptomatic relief.

Outcome: At one-month follow-up, the patient remained symptom-free with normal neurological function, suggesting successful conservative management despite underlying osteoclast dysfunction.

Conclusion: This case highlights an unusual presentation of multilevel spondylolysis with evidence of partial pars remodelling in a mild variant of osteopetrosis. Recognition of such atypical reparative changes expands the phenotypic spectrum of osteopetrosis and emphasises the potential for conservative management in select mild cases.