Persistent nodules at injection sites (aluminium granuloma)—clinicopathological study of 14 cases with a diverse range of histological reaction patterns

Abstract

To assess and document the spectrum of histological appearances of persistent swellings which occur at injection sites following vaccination or allergen desensitization. Fourteen cases were studied. Four overlapping histological reaction patterns were evident. Ten cases showed at least focal fibrosis, fat necrosis and a mixed inflammatory cell infiltrate mainly in the subcutis, giving rise to the features of a non-specific septal and lobular panniculitis. The appearance of three cases, in addition to the non-specific panniculitis pattern, also included prominent lymphoid follicles with germinal centres and a prominent perifollicular infiltrate resembling a lymphoma (pseudolymphoma pattern). A single case mimicked lupus profundus, with a perivascular and periadnexal infiltrate in the dermis and hyaline fat necrosis. Three cases showed a predominantly palisaded histiocytic infiltrate surrounding eosinophilic necrobiosis, in a pattern closely resembling deep granuloma annulare or rheumatoid nodule. The remaining case partly showed this appearance, but in combination with panniculitis, thus demonstrating an overlap of patterns. A common feature in all 14 cases was the focal presence of histiocytes with abundant violaceous granular cytoplasm. These were shown to contain aluminium on energy dispersive X-ray microanalysis. Persistent swellings at injections sites show a variety of overlapping patterns, which mimic other conditions. Identification of characteristic histiocytes with violaceous granular cytoplasm is the key distinctive feature allowing the correct diagnosis to be reached.