A 32-year-old Caucasian male presents with low grade fever, cough and generalized malaise. The patient has otherwise been healthy and has no significant medical history. His past surgical history includes tonsillectomy and tympanostomy tube placement at the age of 8. Careful questioning reveals that the patient recently came back from an "outdoor adventure" trip in the Great Lakes, and began feeling sick only after returning. Microscopic examination of a KOH preparation of an exudate specimen reveals a large yeast cell with a single bud. When incubated in a specific medium at 75.2ºF (24ºC), a multicellular structure with branching, tubular cells grows. The patient is most likely infected with which of the following:

Question

A 32-year-old Caucasian male presents with low grade fever, cough and generalized malaise.  The patient has otherwise been healthy and has no significant medical history.  His past surgical history includes tonsillectomy and tympanostomy tube placement at the age of 8.  Careful questioning reveals that the patient recently came back from an "outdoor adventure" trip in the Great Lakes, and began feeling sick only after returning.  Microscopic examination of a KOH preparation of an exudate specimen reveals a large yeast cell with a single bud.  When incubated in a specific medium at 75.2ºF (24ºC), a multicellular structure with branching, tubular cells grows.  The patient is most likely infected with which of the following:

Quizplus · Accepted Answer

Certain fungal species display different morphologic characteristics in different environments. These fungi are "dimorphic," forming molds (with hyphae) in ambient temperatures (25-30ºC) and yeasts (single cells) at body temperature (37ºC). Five species of thermally dimorphic fungi are medically important and tested on the USMLE Step1. A comparison table is provided below for study purposes: 11ec160b_388e_8c4c_9249_73d0393d8fdc_MD0001_00 (Choice A) Aspergillus fumigatus has a mold form only and is not dimorphic. It is seen in biopsy specimens as septate hyphae that form acute angle V-shaped branches. Aspergillus mainly affects immunocompromised patients. (Choice C) Candida albicans is a component of normal human flora. It causes disseminated infections in immunocompromised patients. It is polymorphic, and it is commonly seen as a budding yeast or forming pseudohyphae. True hyphae also occur, usually only when Candida becomes invasive (in early stages, these hyphae can be identified as germ tubes). (Choice D) Cryptococcus neoformans causes meningitis in AIDS patients. This fungus exists in yeast form only. India ink stain of CSF reveals encapsulated yeast. (Choice E) Malassezia furfur causes a cutaneous mycosis (hypopigmented skin patches). KOH preparation of skin scrapings shows short hyphae and spores ("spaghetti and meatballs"). (Choice F) Rhizopus, Mucor, and Absidia are the saprophytic fungi that cause mucormycosis in immunosuppressed patients. Mold forms of Rhizopus and Mucor are found with nonseptate hyphae and wide angle branching (90º). The typical presentation is a paranasal infection in diabetic ketoacidosis patients. Broad non-septate hyphae are seen in tissue specimens. Educational Objective: Dimorphic fungi grow as molds at 25-30ºC and as yeast at body temperature (35-37ºC). Medically important dimorphic fungi include Sporothrix, Coccidioides, Histoplasma, Blastomyces and Paracoccidioides species. __________ References: Coccidioidomycosis and other endemic mycoses in Mexico. (http://www.ncbi.nlm.nih.gov/pubmed/18095755) Clinical and laboratory update on blastomycosis. (http://www.ncbi.nlm.nih.gov/pubmed/20375357)

A 32-Year-Old Caucasian Male Presents with Low Grade Fever, Cough