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Low back pain in a child—a diagnostic dilemma

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Q1: What is the differential diagnosis?

Vertebra plana: differential diagnosis1:

  • Acute lymphoblastic leukaemia.

  • Tuberculosis of the spine.

  • Metastasis from neuroblastoma.

  • Hodgkin's lymphoma.

  • Langerhan's cell histiocytosis.

Q2: What further investigations should be performed?

The further investigations that should be performed are a skeletal survey, bone scan, bone marrow aspiration, and biopsy.

In this patient a skeletal survey showed radiographic features suggestive of diffuse marrow or bone infiltration (figs 1A and B and 2). Diagnosis was confirmed by bone marrow aspiration, biopsy of the ileum, periodic acid staining by cytochemistry and detection of cell marker CD10. Bone marrow aspiration revealed a solidly cellular, hypercellular marrow with a high nuclear to cytoplasmic ratio, a scant rim of basophilic cytoplasm without granules and lacy chromatin without conspicuous nucleoli. A biopsy specimen of the peripheral skeletal lesions showed a “streaming artefact” in these patients.

Figure 1

(A) Plain AP radiograph of the skull and (B) plain lateral radiograph of the skull.

Figure 2

Plain AP radiograph of the wrist.

Q3: What is the treatment of this condition?

Musculoskeletal pain does not respond to salicylate treatment, but improves rapidly with chemotherapy. The chemotherapeutic regimen includes induction therapy, consolidation therapy, and reinduction therapy using drugs like prednisolone, l-asparginase, vincristine, and Adriamycin in combinations.

Discussion

Leukaemia is a haematological disorder that initially may only cause complaints referable to the musculoskeletal system and hence may mimic several orthopaedic conditions when the patient is first seen. This association may lead the patient to seek orthopaedic treatment initially. The orthopaedist, therefore, must recognise the unusual patterns of presentation that characterise leukaemia and maintain a high index of suspicion if the correct diagnosis is to be made promptly.

Radiographic abnormalities of leukaemia that develop at the time of presentation and during the course of the disease are not always pathognomonic as they are seen in wide range of systemic disorders and chronic disease states.2 The peak incidence of acute paediatric leukaemia occurs at approximately 4 years of age with a secondary peak at 15–20 years of age. Boys are more often affected than girls (1.44:1). Clinical manifestations that occur after a decrease in the production of normal blood components include lethargy, pallor, purpura, fever, hepatosplenomegaly, lymphadenopathy, and bleeding.

The features suggestive of acute lymphoblastic leukaemia are3:

  • Pain and swelling non-responsive to salicylates.

  • Hepatosplenomegaly.

  • Severe anaemia.

  • Thrombocytopenia.

  • Characteristic bony changes.

Skeletal lesions occur more often in children most likely due to the effect of cytokines. Involvement of the skeleton has better prognosis but delay in diagnosis has adverse effect on survival.4 Radiographic skeletal changes include: (1)  Osteopenia—resulting from gradual and progressive generalised demineralisation due to an alteration on protein and mineral metabolism or effect of cytokines. A vertebra plana is associated with severe osteoporosis and necessitates an immediate neurological evaluation.4

(2)
Radiolucent metaphyseal bands—originally described by Baty and Vogt and is a non-specific finding also seen in other chronic childhood diseases. Generalised metabolic dysfunction interfering with the proper osteogenesis of the epiphyseal growth plate results in transverse zones of diminished density.

(3)  Periosteal bone formation—resulting from the lifting of the periosteum from the centre by the leukaemic infiltrate.

(4)
Osteolytic lesions—producing a “moth eaten” appearance common in the metaphysis of the long bones and flat bones. These lesions are predisposed to pathological fractures.
(5)
Osteosclerosis—in the metaphysis of long bones is mostly a late manifestation.
(6)
Mixed lesions—result from both osteoblastic and osteoclastic activity.
(7)
Permeative pattern—indicates an aggressive lesion with rapid growth.
(8)
Pathological fracture—in association with osteoporosis results in vertebra plana.

In India and other Asian countries tuberculosis of the spine accounts for 50% of skeletal tuberculosis.5 Lumbar spine involvement is only second in common after lower dorsal spine. A central type of involvement results in vertebral collapse and a vertebra plana-like picture. Usually, the disc space is reduced in association, which is a distinctive feature. Spinal tuberculosis is common both in children and adults and in support with the laboratory investigations may precede as the most likely diagnosis over other local or systemic inflammatory conditions.

As the initial presentation of leukaemia commonly involves the musculoskeletal system, the clinician therefore must include acute leukaemia in the differential diagnosis of any child with unexplained radiographic skeletal pathology.

Final diagnosis

Acute lymphoblastic leukaemia causing osteopenia.

Acknowledgments

We thank the Dean, KEM Hospital and Seth G S Medical College for granting us permission to use hospital data.

References

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