histoplasmosis is an infectious disease caused by the dimorphic fungus Histoplasma capsulatum, which is endemic to the Ohio and Mississippi River valleys and thrives in soil contaminated with bird or bat droppings. While the majority of acute infections are asymptomatic or present as a self-limiting respiratory illness, the organism can evade macrophage destruction and disseminate, particularly in immunocompromised hosts (such as those with HIV or on immunosuppressive therapy). The underlying pathological mechanism involves a granulomatous inflammatory response, which can lead to caseating or non-caseating granulomas in the lungs, liver, spleen, and lymph nodes. Clinically relevant subtypes frequently encountered in coding include acute pulmonary histoplasmosis (B39.0), severe disseminated histoplasmosis (B39.3), and Presumed Ocular Histoplasmosis Syndrome (POHS), which causes chorioretinal scarring and secondary neovascularization (B39.9 and H32). It is commonly confused with coccidioidomycosis and blastomycosis; however, histoplasmosis is uniquely characterized by its intracellular parasitism of macrophages and its specific geographic endemicity in the Midwestern and Central United States.
Noun-forming suffix — “state or condition of,” usually denoting an abnormal or diseased state
The word entered English in the 1900s (specifically 1906) as histoplasmosis (noun), coined by American pathologist Samuel Taylor Darling. Darling discovered the organism in the tissues of a patient in Panama and named it Histoplasma capsulatum — literally “encapsulated substance formed in tissue.” He erroneously believed the organism was a protozoan (like Leishmania) that invaded the cytoplasm of tissue macrophages, hence the name. The root plasma (“something formed”) connects histoplasmosis to the entire -plasm family: neoplasm (new formation → tumor), cytoplasm (cell substance → intracellular fluid), and hyperplasia (excessive formation). The prefix histo- is highly productive in medical terminology, appearing in histology, histopathology, and histamine.
🔀 ALIASES / ALTERNATE TERMS
Darling’s disease(historical eponymous term; rarely used in modern clinical documentation but found in older literature)
Cave disease / Spelunker’s lung(lay/environmental synonyms; highlights the risk of exposure to bat guano in caves)
Ohio Valley disease(geographic synonym; denotes the primary endemic region in the United States)
Presumed Ocular Histoplasmosis Syndrome (POHS)(ophthalmologic manifestation; characterized by “histo spots,” peripapillary atrophy, and choroidal neovascularization)
Disseminated histoplasmosis(severe systemic form; typically seen in immunocompromised patients, coded to B39.3)
Chronic cavitary histoplasmosis(pulmonary subtype; often seen in older patients with underlying COPD, mimicking tuberculosis)
Laryngeal histoplasmosis(anatomic subtype; presents with hoarseness and vocal cord lesions that can clinically mimic squamous cell carcinoma)
🔗 RELATED TERMS
Coccidioidomycosis — a distinct endemic fungal infection (Valley fever) caused by Coccidioides; distinguished by its geographic distribution (Southwestern US) and formation of spherules rather than intracellular yeast.
Blastomycosis — another endemic dimorphic fungus; distinguished by broad-based budding yeast and a higher propensity for skin and bone involvement.
Tuberculosis — a mycobacterial infection that closely mimics the clinical and radiographic presentation of pulmonary histoplasmosis, including cavitary lesions and granuloma formation.
Choroidal Neovascularization — the growth of new, abnormal blood vessels in the choroid; a sight-threatening complication of POHS requiring intravitreal anti-VEGF therapy.
Granuloma — the cellular mechanism/lesion formed by macrophages and epithelioid cells attempting to wall off the Histoplasma organisms.
Macrophage — the primary host cell for Histoplasma capsulatum, which survives and replicates within the phagolysosome of this immune cell.
Erythema Nodosum — an inflammatory condition of the subcutaneous fat (panniculitis) that can occur as an immunologic reaction to acute histoplasmosis (L52).
Antibody; histoplasma (Serologic testing for diagnosis)
⚠️ Coding Note: For inpatient profee coding under Noridian MAC (JE/JF), strict adherence to sequencing rules is critical when histoplasmosis is a manifestation of an underlying immune deficiency. If a patient is admitted for disseminated histoplasmosis (B39.3) and has symptomatic HIV/AIDS, B20 (Human immunodeficiency virus [HIV] disease) must be sequenced as the principal diagnosis, followed by B39.3. For Presumed Ocular histoplasmosis Syndrome (POHS), etiology/manifestation convention requires coding the underlying infection (e.g., B39.9) first, followed by H32 (Chorioretinal disorders in diseases classified elsewhere). An undercoding alert for Ophthalmology coders: when billing 67028 for intravitreal injections to treat POHS-related choroidal neovascularization, ensure the specific HCPCS J-code for the anti-VEGF agent (e.g., J2778 for ranibizumab) is billed with the exact number of units administered, and append the appropriate laterality modifiers (-RT, -LT, or -50) to both the surgical CPT and the medication code to prevent MAC denials.