# Fulminant Disseminated Coccidioidomycosis With Histoplasma Antigen Cross-Reactivity

## TL;DR

An elderly man with diabetes and a blood disorder died from a severe fungal infection that was misdiagnosed due to a cross-reactive test result.

## Contribution

This case highlights the risk of fulminant coccidioidomycosis and the potential for cross-reactivity in Histoplasma antigen tests.

## Key findings

- The patient had positive Histoplasma antigen and Coccidioides antibody tests, but the infection was caused by Coccidioides immitis.
- The patient's rapid clinical decline and imaging findings were consistent with disseminated coccidioidomycosis.
- The case underscores the importance of recognizing risk factors and limitations of serologic testing for fungal infections.

## Abstract

A 79-year-old man with type II diabetes mellitus and recently diagnosed idiopathic thrombocytopenic purpura presented to the Emergency Department with progressive dyspnea over the course of two weeks. He was found to have diffuse miliary nodules, dense cavitary consolidation, and widespread cystic changes on chest imaging and died within 48 hours of admission to the hospital. His serum Coccidioides antibody and urine Histoplasma antigen were both positive. He later grew Coccidioides immitis from the blood, supporting the theory that Histoplasma positivity was likely the result of antigen test cross-reactivity. Coccidioidomycosis typically presents with mild, self-limited symptoms, but may also disseminate rapidly, causing fulminant, life-threatening disease. Prompt recognition of risk factors for fulminant coccidioidomycosis and understanding flaws in serologic testing are essential to the appropriate diagnosis and management of this disease.