Background IgG4-related systemic fibrosclerosis is a recently defined disorder characterised by a diffuse or tumefactive inflammatory reaction rich in IgG4-positive plasma cells associated with sclerosis and obliterative phlebitis. Although characteristic histopathological features are essential for the diagnosis of these disorders, to date there exists no consensus regarding the cut-off values used to define a 'significant IgG4-positive plasma cell count,' and data regarding the distribution of IgG4-positive plasma cells under common (non-specific) inflammatory conditions are lacking. Methods The authors analysed 121 randomly selected histopathological specimens containing prominent lymphoplasmacytic infiltrates (11 obstructive sialadenitis, 27 inflammatory lesions of the oral cavity, 24 inflammatory gastrointestinal lesions, 15 rheumatoid synovitis, 15 non-specific synovitis, eight non-specific dermatitis and 21 primary carcinomas with a peritumoral inflammatory response). For comparison, seven cases of sclerosing sialadenitis (Küttner tumour) were examined. Results High counts of IgG4 plasma cells were found in sclerosing sialadenitis (mean 40/high-power field (hpf)), contrasting sharply with sialadenitis caused by sialolithiasis (mean 3/hpf). Greatly varied but generally high counts of IgG4-positive plasma cells were also seen in several of the other lesions, particularly in rheumatoid synovitis (mean 55/hpf), oral cavity lesions (mean 79/ hpf) and carcinoma-associated inflammatory response (mean 24/hpf). The mean IgG4/IgG ratios for all lesions varied between 0 and 0.4. Conclusions The results demonstrate the ubiquitous occurrence of variably high numbers of IgG4-positive plasma cells under diverse non-specific inflammatory conditions, indicating that high IgG4-positive plasma cell counts and high IgG4/IgG ratios per se do not reliably distinguish IgG4-associated systemic disease from nonspecific conditions, and that the IgG4 counts must be cautiously interpreted in the context of appropriate clinical and histopathological features.

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Symptomatic gout tophi of the spine are a rare but well-characterized complication of tophaceous gout. The authors report the case of a 29-year-old previously healthy man who presented with L-5 radiculopathy. Lumbar magnetic resonance (MR) imaging revealed a 4.5 x 4.5 x 2.8-cm large gout tophus mimicking a malignant spinal tumor or abscess. The tophus completely destroyed both L-4 and L-5 facet joints and the left L-4 lamina and spread epidurally from L-3 to L-5, compressing the left L-5 nerve root. There has been no similar case reported so far with respect to the extent of bone destruction. The authors describe the case history and present intraoperative, MR imaging, and histological findings.

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