Chest x-ray and CT of the thorax displayed a right paratracheal mass and suggested right brachiocephalic vein infiltration/compression. An abdominal CT scan confirmed hepatosplenomegaly and retroperitoneal lymphadenopathy. There was no evidence of malignancy demonstrated in bronchoscopic samples (brushings/washings from right upper lobe), fine-needle aspiration from a cervical lymph node, or a mediastinoscopic nodal biopsy. The latter two specimens displayed occasional non-necrotising granulomata. Blood tests showed a C-reactive protein of 106 mg/litre and a white cell count of 13.4×109 cells/litre. Lactate dehydrogenase concentration was normal. A HIV test was negative, no immunoglobulin deficiency was identified, complement levels were normal, and although CD4 count was within normal range (0.46×109 cells/litre), CD8 levels were reduced at 0.15×109 cells/litre.
A radionuclide bone scan was non-diagnostic of a cause for hypercalcaemia. Renal ultrasound identified no obstruction, and blood, urine and stool cultures showed no significant growth.
Sputum microscopy demonstrated numerous AAFBs confirmed as belonging to Mycobacterium tuberculosis complex by PCR. Later, prolonged sputum solid media culture demonstrated growth of M microti, sensitive to pyrazinamide, rifampicin, ethambutol and isoniazid.
Biopsy obtained at mediastinotomy was macroscopically compatible with an enlarged lymph node. Microscopic appearances () were of a multinodular proliferation of spindle cells with moderate numbers of interspersed small blood vessels, admixed with numerous lymphocytes and plasma cells. The lesion almost obliterated the nodal architecture leaving only a thin rim of normal residual lymphoid tissue. A few peripheral multinucleate giant cells and sparse aggregates of macrophages constituting poorly formed non-necrotic granulomata were identified. There was no evidence of malignancy.
Histology of biopsy displaying mycobacterial spindle cell pseudotumour.
Spindle cells were CD68 positive on immunohistochemistry, confirming a macrophage-monocyte derived phenotype. Ziehl–Neelsen staining demonstrated numerous clusters of curved AAFB within spindle cells throughout the lesion (). Many cells showed cytoplasmic distension due to the large number of organisms. The histopathological appearances were those of a mycobacterial spindle cell pseudotumour (MSCP) and immunohistochemistry excluded other possibilities such as metastatic malignancies with a spindled morphology.
Ziehl–Neelsen stained biopsy sample demonstrating numerous curved acid and alcohol fast bacilli.
In January 2007 a pregnant alpaca on a farm close to the patient’s residence developed diarrhoea and weight loss. Despite veterinary attention the alpaca’s condition deteriorated and she aborted on 19 March and died on 22 March 2007. A postmortem carried out by the Scottish Agricultural College showed both lungs were collapsed and oedematous containing a single abscess without evidence of pneumonia. In the abdomen there was a massive quantity of pale yellow fluid with extensive fibrin deposits arising from multifocal abscesses or tumour formation in the liver. These liver lesions contained central necrotic or inspissated areas and extended onto the serosal surface of the duodenum. Ziehl–Neelsen-stained smears of the liver lesions demonstrated numerous AAFBs resembling Mycobacterium spp. Genotyping confirmed the presence of M microti.
DNA was extracted from the human isolate at the Scottish Mycobacteria Reference Laboratory (SMRL), Edinburgh, UK and from the alpaca isolate at the Veterinary Laboratory Agency (VLA), Weybridge, UK. At SMRL spoligotyping was performed using a commercial assay available from Isogen Life Science (3600 BT; Maarssen, The Netherlands) and 15-locus Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem Repeat (MIRU-VNTR) typing, performed using the current strategy for M tuberculosis
Spoligotyping and VNTR typing using six exact tandem repeat (ETR) loci (ETR-A to ETR-F) were performed on both isolates at VLA. The strains were indistinguishable by both methods. The spoligotype pattern was designated SB0112 by http://www.mbovis.org
(VLA type 19). The 15-locus MIRU-VNTR profile was 123571 210414 23232 and the 6-locus ETR result was 12-3-5-7*-4-2.2. Both strains were deleted for RDmic
, which identifies them as members of the M microti
Additionally, around the time of the patient’s illness, she adopted a stray cat that had been unwell with vomiting. The cat survived, but unfortunately no samples were available from this animal.