Persistent subcutaneous nodules in patients hyposensitized with aluminum-containing allergen extracts

The development of persistent nodules that cause pain and itching at a vaccination or hyposensitization injection site is a rare event. These lesions have been mainly attributed to a hypersensitivity reaction to aluminum hydroxide, which is used as an absorbing agent in many vaccines and hyposensitization preparations. Patch tests with standard antigens and aluminum compounds and histopathologic and ultrastructural studies were performed on 10 patients with persistent subcutaneous nodules on the upper part of their arms after injection of aluminum-adsorbed dust and/or pollen extracts.

The nodules appeared 1 month to 6.5 years after injections. The results of patch tests with 2% aluminum chloride were positive in five patients. Histopathologic examination revealed two different patterns: some biopsy specimens (from lesions of less than 9 months' duration) showed a pure foreign body histiocytic reaction characterized by extracellular amorphous dermal basophilic deposits with a histiocytic-macrophagic reaction; others showed a delayed hypersensitivity granulomatous reaction in association with an histiocytic foreign body response. The lesions were characterized by a unifocal or multifocal unencapsulated granulomatous reaction in the deep dermis and/or subcutaneous tissue. Eosinophilic necrotic areas surrounded by dense fibrous bands and a massive inflammatory infiltrate (lymphoid follicles, large histiocytic cells, abundant eosinophils, and some plasma cells) were observed. A granular basophilic material in extracellular spaces and within the cytoplasm of some histiocytes was also noted. Electron microscopic studies revealed intracytoplasmic and extracellular deposits of a fibrillar electron-dense material.

Persistent subcutaneous nodules that develop after the administration of aluminum-containing preparations may show two characteristic histopathologic patterns. A pure histiocytic foreign body reaction was observed in early lesions, and a delayed hypersensitivity granulomatous reaction was seen in older lesions. No relationship between histopathologic pattern and patch test results was observed. Aluminum-free preparations should be used in patients in whom these nodules develop.