Which histologic findings are diagnostic of coccidioidomycosis?

Updated: Aug 27, 2019
  • Author: Duane R Hospenthal, MD, PhD, FACP, FIDSA, FASTMH; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

The diagnosis of coccidioidomycosis can be made by observing spherules (≤70 μm in diameter) that contain endospores in specimens of any body fluid, including sputum or lesion smears and biopsy material. (See the images below.) Direct examination of sputum is less sensitive than cultures for the identification of spherules.

Sputum smears can be stained with potassium hydroxide [KOH]. Spherules are also identified on smears by using calcofluor white or cytologic stains. Spherules are identified in biopsy specimens using standard stains such as hematoxylin and eosin or Papanicolaou stains. Other useful stains for tissue specimens include periodic acid-Schiff stain (PAS) or Gomori methenamine silver stain.

Pulmonary cocci spherule (Hematoxylin-eosin stain) Pulmonary cocci spherule (Hematoxylin-eosin stain).
Pulmonary cocci spherule, periodic acid-Schiff sta Pulmonary cocci spherule, periodic acid-Schiff stain.

The predominant tissue reaction is granulomatous. In acute lesions, macrophages and polymorphonuclear neutrophils may be numerous. As lesions become chronic, fibrosis ensues. Caseation and, rarely, calcification may occur.

Coccidioidal spherules rupturing and releasing end Coccidioidal spherules rupturing and releasing endospores. Gomori methenamine silver (GMS) stain. Photograph by Joseph Rabban, MD.
A granuloma with coccidioides immitis spherule (pr A granuloma with coccidioides immitis spherule (pretracheal lymph node biopsy).
A ruptured Coccidioides immitis spherule (pretrach A ruptured Coccidioides immitis spherule (pretracheal lymph node biopsy).
Gomori methenamine silver stain of Coccidioides im Gomori methenamine silver stain of Coccidioides immitis spherule (pretracheal lymph node biopsy).
Periodic acid-Schiff stain of Coccidioides immitis Periodic acid-Schiff stain of Coccidioides immitis spherule (pretracheal lymph node biopsy).

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