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Case Report | Discussion

Case report:

A six-year-old boy was hospitalized for progressive weakness in both lower limbs since one week. At neurological assessment, the plantars were upgoing and the power in the lower limbs, initially graded as 3, had decreased significantly on re-examination a few days later. There was no evidence of a swelling or tenderness along the spine. The patient also complained of painful swelling over the left scapula since one month (Fig 1). On examination, the swelling was found to be approximately 8 cm in size, firm, warm and tender. The child was afebrile and had no constitutional symptoms. The blood profile revealed a hemoglobin level of 13.2g% and an elevated ESR of 50mm/hr. The child tested negative for HIV.

Fig 1

The plain frontal radiograph of the left scapular region was taken (Fig. 2). It showed in a lytic, expansile lesion showing multiple internal septations within, involving the scapula. The lesion showed a narrow zone of transition. There was no periosteal reaction or surrounding soft tissue involvement. Other visualized bones appeared unremarkable.

Fig 2

The plain radiograph of cervical spine (Fig.3) was essentially unremarkable.

Fig 3

A CT scan of the thorax was done (Fig 4a and b), which showed a homogeneous soft tissue density causing expansion of the left scapula. There is cortical thinning and discontinuity at multiple places, though obvious extension into surrounding soft tissues is not seen.

Fig 4a	Fig 4b

Similar destructive lesion is also noted involving the vertebral body and left posterior vertebral elements. This soft tissue lesion is seen to encroach upon the spinal canal.

On MRI (Fig 5a and b), the expansile lesion is seen involving the whole of the scapula except the inferior angle. The lesion is hypointense on T1W image and heterogeneously hyperintense on T2W image. No extension of the lesion in the left shoulder joint or surrounding soft tissues is seen.

Fig 5a	Fig 5b

The MRI of the spine (Fig 6a and b) shows marked destruction of 2nd and 3^rd dorsal vertebrae and intervening disc space, with anterior wedging and anterolisthesis of D2 over D3. Abnormal extradural soft tissue is seen along with gibbus (at the same level) causing compression of the spinal cord. The cord however shows normal signals .An abnormal prevertebral soft tissue with a small abscess was also noted.

Fig 6a	Fig 6b

The patient also developed a firm to soft swelling over the forehead. The plain frontal radiograph of the skull (Fig 7) revealed well-circumscribed lytic lesions in the calvarium without evidence of marginal sclerosis.

Fig 7

Differential diagnosis: Looking at the individual lesions suggest number of differentials for each of the lesions. Like multiple lytic lesions in this age group could represent inflammatory conditions like osteomyelitis (tuberculous or pyogenic) or neoplastic like eosinophillic granuloma or round cell tumors (like neuroblastoma, lymphoma or leukemia). But observing all these lesions simultaneously precludes all other differentials except tuberculosis. This is in accordance with ‘Law of Parsimony’, which states that in patients with multiple lesions, a single etiologic factor is responsible for all the lesions in most cases.

Histopathology : Pathological examination of scrapings from the scapula revealed the presence of caseous material and epitheloid cells with fragments of necrotic bone along with the normal bone. Few langerhans type of giant cells (arrow) were also seen (Fig. 8).

Fig 8

Diagnosis: Multifocal cystic tuberculosis.

Operative and postoperative course: At surgery laminectomy of the D2 and D3 vertebrae was performed to decompress the spinal cord at that level. Gross destruction of the bodies and the posterior elements of these vertebrae mainly on the left side corroborated the MRI findings. Pathological examination of the frozen section of the necrotic material evacuated from the spinal canal showed the presence of multi-nucleated giant epitheloid cells and fragments of necrotic bone. Posterior fixation of the vertebral column was achieved with Hartshill’s rods (Fig.9). Anterior bone grafting and fixation were planned for later. The boy was started on a multidrug antituberculous regimen.

Fig 9

Discussion

Tuberculosis is caused by Mycobacterium tuberculosis. It may be uncommon in Western world but it is still quite rampant in developing countries where it is endemic. Even in the Western world it has staged a resurgence now, due to rampant spread of HIV infection

TB of the skeletal system is far less commonly encountered than pulmonary infection and represents 1-2 % of TB overall, or 10–20 % of extra pulmonary manifestations of this disease (3,4,5). Multifocal bone involvement is seen in 5-10 %of skeletal TB, most often seen with concomitant pulmonary infection. Systemic manifestations usually occur in the presence of concomitant pulmonary disease.

Tuberculous infection of the bone is thought to result from primary infection, which comprises of Ghon’s foci in the lungs. The bacilli are seeded not only to the lungs but also to different organs including bone where they remain dormant until reactivation occurs. The outcome of the lymphatic and hematogenous spread of the bacilli is determined by the number of organisms released and by host resistance.

Multifocal skeletal TB is a well-recognised pathological entity. These lesions are found at different stages of development owing to a haematogenous mode of spread by which bacilli are seeded at different times to different sites in the skeleton. A suppressed host immune response predisposes to multiple bone lesions. Solitary bone lesions in TB though less common have been more frequently encountered in recent years. These are thought to result from sensitization to the bacilli before skeletal dissemination occurs.

Skeletal TB characteristically causes lesions in bone that are lytic and generally lack sclerosis, sequestra and periosteal reactions. In skeletal TB sequestration is relatively uncommon and less extensive than in pyogenic osteomyelitis. Further, a more rapid course and a less frequent extension of the inflammatory process across the metaphysis or to the neighboring joint in pyogenic infection, serves to differentiate it from TB.

In osseous TB, the axial skeleton is the most frequently involved. The spine is affected in about half the cases. The commonest location is in the dorsolumbar spine. In TB of the spine there is considerable destruction of the vertebral bodies and a loss of the intervertebral disc space with large paravertebral abscesses.

Cystic tuberculosis is a rare but well recognised variant reported first by Jungling in early part of 20^th century. He called it ‘Osteitis tuberculosa multiplex cystoides’. It is also called Jungling’s disease after him. Though it was proved later that what he described was actually sarcoidosis. Cystic tuberculosis is seen much more commonly in children. In children such cystic lesion usually but not invariably involves metaphysis of peripheral tubular long bones. These lesions may be symmetric in distribution and unaccompanied by sclerosis. On the contrary in the adults axial skeletal (skull, shoulder, pelvic girdle) is more frequently involved and lesions possess well-defined margins with sclerosis.

Disseminated lytic skeletal lesions in children, as in other age groups, raise the differential of a number of conditions most of which can be categorized as inflammatory (e.g. pyogenic osteomyelitis, syphilis, blastomycosis and coccidioidomycosis) or neoplastic e.g. eosinophil granuloma (EG) and some small cell tumours of bone like neuroblastoma and non-Hodgkin’s lymphoma.

Eosinophil Granuloma with a predilection for males between 3 and 12 yrs of age, mainly affects the skull. The skull, ribs, pelvis and femur between them account for about two thirds of all cases. Multiple lesions are seen in about 10% cases at first presentation. Unlike in TB, the skeletal lesions in EG do not commonly involve the spine and the affected sites in bone are generally mildly painful and tender. While bone lesions in TB can be tender on examination, they are seldom otherwise painful. Lesions with sharply defined margins in EG show an absence of a periosteal reaction and of sclerosis and can thus be mistaken for TB. Button sequestra may even be observed in some of these cases. However in EG, scalloped margins of the lesions, a relative absence of soft tissue and involvement of the inner and outer tables of the skull to different degrees in calvarial lesions can to some extent help in differentiating these lesions from those of tubercular etiology.

Bone lesions in neuroblastoma can on occasion be confused for TB. However, a majority of these cases is seen under the age of 5 yrs. Permeative bone destruction rather than sharply defined lytic foci characterizes most of the lesions in neuroblastoma. Long bone involvement (particularly the femur and tibia) can often be bilaterally symmetric . Enhancing soft tissue masses are seen with some of the bone lesions and can produce a striking appearance in the skull where lytic foci in the calvarium are seen alongside large enhancing extradural and scalp masses. Further, intracranial metastases and apparent sutural separation, which results from metastatic deposition of tumour cells, help characterize the lesion. Metastasis to the spine is frequent and can sometimes result in cord compression. However, unlike TB, compressive myelopathy is rarely seen as an initial finding in neuroblastoma. Bone marrow aspiration and elevated urine VMA and catecholamine metabolites in most cases serve to detect the presence of a neuroblastoma.

In flat bones (e.g. the sternum and the scapula) or within the metaphyses of long bones expansile cystic lesions can be confused with aneurysmal bone cysts and more so if they have a trabeculated /multiloculated configurations as in the lesions seen in our case. The likelihood of misdiagnosing the scapula lesions seen in these cases for bone cysts was largely precluded by the presence of other skeletal lesions.

The definitive diagnosis of tuberculosis can only be made on histopathological evaluation of the tissue specimen. These specimens usually reveal granulomatous inflammatory changes including multinucleated giant cells, epitheloid cells and typical tuberculoid granulomas with foci of caseous necrosis.

Radiologically skeletal survey remains the first line of investigations for determination of the extent of the disease. CT and MRI to locate define the extent and nature of the bone lesions can follow this. They also help in evaluating the extent of the surrounding soft tissue involvement. Spine evaluation in particular has been revolutionized with the help of MRI. Bone scan has been disappointing in evaluation of the tuberculous lesions due to, unacceptably high false negative rate and lack of additional information provided by them.

With advent of modern anti-tubercular drugs, cystic tubercular lesions are known to respond quite well to the conservative medical treatment. However definitive surgical intervention is warranted for spine lesions where spinal cord compromise is a feature, in our case. Usually cord decompression with; stabilization of spine with the help of prosthesis or bone grafts is done.