Abstract

     A 62-year-old man presented to the emergency department for evaluation of superficial abrasions on his arms, legs, and face following “significant tree work.” Because of recent travel to the Dominican Republic, the patient believed he had myiasis. One right neck lesion became inflamed and tender, with drainage. The condition did not respond to several courses of oral and topical antibiotics. The initial biopsy showed granulation tissue with multinucleated giant cells and numerous small tubular structures that were mildly refractile upon polarization. Well-formed granulomas were absent and chitin was not seen. Since the refractile material was deemed compatible with myiasis fly body parts by the original pathologist, the patient received ivermectin. Two months later, despite treatment, the patient developed new lesions on the right neck and left upper lip, with no recollection of injury. A biopsy specimen from the upper lip revealed dermal fibrosis with fibrinoid necrosis and identical structures interspersed within the interstitium and within giant cells. These hollow, cylindrical structures were studded with regular spine-like protrusions. Our differential included caterpillar setae, foreign medical material and diatoms. Curiously, upon specific questioning, the patient confirmed applying “medical grade” diatomaceous earth to his open wounds. Diatoms are a major group of algae with cell walls composed of silica. We believe this explains the observed refractility. Diatoms are a fossilized constituent of diatomaceous earth. Lack of familiarity with their characteristic appearance may lead to a misdiagnosis of infection, even among seasoned dermatopathologists.