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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Dermatology · Chromoblastomycosis

How Chromoblastomycosis is Diagnosed

At a Glance

Chromoblastomycosis is confirmed when characteristic muriform, or sclerotic, fungal bodies are found in a skin scraping or biopsy. KOH testing, special stains, culture, and sometimes PCR help identify the infection and distinguish it from skin cancer and other look-alikes.

Confirming a diagnosis of chromoblastomycosis is often a process of elimination. Because it grows so slowly and can look like many other skin conditions, doctors must look for very specific microscopic clues to separate it from its “look-alikes” [1][2].

The Diagnostic Gold Standard

The single most important piece of evidence in your diagnosis is the discovery of muriform cells (also called sclerotic bodies, Medlar bodies, or copper-penny bodies) [3][4]. These are thick-walled, chestnut-brown fungal cells that represent the fungus in its parasitic state. If these cells are found, the diagnosis of chromoblastomycosis is confirmed [5].

Your medical team will typically use three main tools to investigate the skin:

  1. KOH Preparation (Scraping): Your doctor may use a scalpel or slide to gently scrape the “black dots” or crusty areas on your lesion [6]. These scrapings are mixed with a chemical called potassium hydroxide (KOH) and viewed under a microscope. This is a rapid bedside test that can sometimes provide an answer within minutes if muriform cells are visible [7][8].
  2. Skin Biopsy: A deeper sample of skin is usually required. A doctor will typically use a “punch biopsy” to remove a small cylinder of tissue. A pathologist will use special stains—most commonly PAS (Periodic Acid-Schiff) or GMS (Grocott-Gomori Methenamine Silver)—to make the fungal cells stand out from your own tissue [9][10].
  3. Fungal Culture: A piece of your tissue is placed in a special dish in a lab to see if the fungus will grow. This can help identify exactly which species of fungus is causing the infection. However, the fungus grows extremely slowly and cultures are often negative [6][11].

If tests are negative but symptoms persist, an experienced dermatologist or dermatopathologist may need to repeat the biopsy. In well-equipped reference laboratories, newer molecular testing (PCR) is sometimes used as an adjunct to identify the fungal DNA, though availability varies and a negative PCR does not automatically mean you don’t have the disease [12][13].

The “Look-Alikes”

Because chromoblastomycosis is rare in some parts of the world, it is often mistaken for more common conditions. Your doctor will need to rule out these clinical mimics:

  • Sporotrichosis: Often called “rose gardener’s disease,” this infection usually creates a chain of bumps that follow the path of your lymph nodes, whereas chromoblastomycosis tends to stay as localized, warty plaques [14][15].
  • Tuberculosis Verrucosa Cutis: A form of skin tuberculosis that creates similar warty growths. It requires different stains and testing to distinguish from a fungal infection [15].
  • Mycetoma: This condition also causes swelling and bumps, but it is characterized by “grains” (visible clumps of organisms) that drain from small holes (sinus tracts) in the skin. Chromoblastomycosis does not produce these grains [16][17].
  • Squamous Cell Carcinoma (SCC): This is a type of skin cancer. Longstanding chromoblastomycosis can cause the skin to react in a way called pseudoepitheliomatous hyperplasia, which looks very similar to SCC under a microscope [18][2]. It is vital for a pathologist to determine if the growth is just a reaction to the fungus or if the chronic infection has actually turned into cancer [19].

Reading Your Pathology Report

When you receive your pathology results, look for these specific terms and phrases:

Look for these terms What they mean
Muriform / Sclerotic bodies The definitive fungal cells that confirm the diagnosis [5].
Medlar / Copper-penny bodies Other names for the characteristic brown fungal cells [3].
Dematiaceous fungi Refers to the “dark-walled” family of fungi that cause this disease [20].
Granulomatous inflammation A specific pattern of immune response where the body tries to “wall off” the fungus [21].
Pseudoepitheliomatous hyperplasia An overgrowth of the top layer of skin; often seen as a reaction to the infection [22].
PAS or GMS positive Indicates that the special fungal stains successfully highlighted organisms in the tissue [10].

Common questions in this guide

What finding confirms chromoblastomycosis?
The diagnosis is confirmed when muriform cells—also called sclerotic, Medlar, or copper-penny bodies—are found in a skin scraping or biopsy. These thick-walled, brown fungal cells are the characteristic form of the organism in tissue.
How do doctors test for chromoblastomycosis?
Doctors may begin with a KOH preparation of material scraped from the lesion, which can show muriform cells quickly. A punch biopsy is often used for deeper tissue and special PAS or GMS stains, while fungal culture may identify the species; PCR is sometimes added.
Can I still have chromoblastomycosis if my fungal culture is negative?
Yes. Chromoblastomycosis fungi grow very slowly, so cultures can be negative even when infection is present. If suspicion remains, a clinician may review or repeat the biopsy and consider PCR where available.
Does pseudoepitheliomatous hyperplasia mean I have skin cancer?
Not necessarily. Pseudoepitheliomatous hyperplasia is an overgrowth of the surface skin that can occur as a reaction to infection and can resemble squamous cell carcinoma. A pathologist must determine whether it is only a reactive change or whether cancer is also present.
What other conditions can look like chromoblastomycosis?
Sporotrichosis, tuberculosis verrucosa cutis, mycetoma, and squamous cell carcinoma can resemble chromoblastomycosis. Doctors compare the lesion pattern and laboratory findings; for example, mycetoma may produce draining grains, while chromoblastomycosis is associated with muriform bodies.

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Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Did you see 'muriform cells' or 'sclerotic bodies' on my biopsy or KOH scraping?
  2. 2.Since my fungal culture was negative, can we send my biopsy tissue for molecular testing (PCR) to help identify the specific fungus?
  3. 3.Is the 'pseudoepitheliomatous hyperplasia' on my report a sign of fungal infection, or do we need to rule out squamous cell carcinoma?
  4. 4.What stains were used on my biopsy—specifically, were PAS or GMS stains performed to highlight fungal cells?
  5. 5.Could my symptoms be explained by another condition like sporotrichosis or mycetoma, and how did we rule those out?

References

References (22)
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    Chromoblastomycosis in Latin America and the Caribbean: Epidemiology over the past 50 years.

    Guevara A, Siqueira NP, Nery AF, et al.

    Medical mycology 2021; (60(1)) doi:10.1093/mmy/myab062.

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    The Role of Excision for Treatment of Chromoblastomycosis: A Cutaneous Fungal Infection Frequently Mistaken for Squamous Cell Carcinoma.

    Rolon AM, Tolaymat LM, Sokumbi O, Bodiford K

    Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.] 2023; (49(7)):649-653 doi:10.1097/DSS.0000000000003800.

    PMID: 37093678
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    [Chromoblastomycosis].

    Molochkov VA, Khlebnikova AN, Petrova MS, Bobrov MA

    Arkhiv patologii 2020; (82(6)):59-62 doi:10.17116/patol20208206159.

    PMID: 33274629
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    Combination therapy for an elderly patient with chromoblastomycosis caused by Fonsecaea monophora: a case report.

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    Annals of translational medicine 2022; (10(2)):114 doi:10.21037/atm-21-6119.

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    In Vitro Activities of Five Antifungal Drugs Against Conidia and Sclerotic Cells of Chromoblastomycosis Agent Fonsecaea spp.

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    Microbiology and immunology 2026; (70(3)):139-147 doi:10.1111/1348-0421.70038.

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    Chromoblastomycosis: A Case Series and Literature Review.

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    Indian dermatology online journal 2023; (14(5)):665-669 doi:10.4103/idoj.idoj_292_23.

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    First Japanese Case of Chromoblastomycosis Caused by Phialophora europaea.

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    Chromoblastomycosis Presenting with Sporotrichoid Distribution and Bony Destruction: A Rare Presentation.

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    Secondary Myiasis in an Immunocompetent Patient With Severe Chromoblastomycosis.

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    Accuracy of direct examination and culture as compared to the anatomopathological examination for the diagnosis of chromoblastomycosis: a systematic review.

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    Molecular identification of Fonsecaea pedrosoi in chromoblastomycosis: Insights from paraffin-embedded human skin biopsies and clinicopathology.

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    Medical mycology 2025; (63(7)) doi:10.1093/mmy/myaf055.

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    Molecular identification of chromoblastomycosis clinical isolates in Guangdong.

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    Lymphocutaneous Sporotrichosis of Face with Verrucous Lesions: A Case Report.

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    Successful treatment of tuberculosis verrucosa cutis with fester as primary manifestation with photodynamic therapy and anti-tubercular drugs.

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    Deep Fungal Infections of Skin and Role of Histopathology in Diagnosis.

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    Concurrent chromoblastomycosis and eumycetoma: a unique case of dual neglected tropical fungal diseases in Asia.

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    Squamous cell carcinoma in chronic lesions of recalcitrant chromoblastomycosis. Study of ten patients treated at the Dermatological Center of Yucatán, Mexico.

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    An impressive case of chromoblastomycosis due to Fonsecaea pedrosoi in a patient with a long history of fungal infection.

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This page explains chromoblastomycosis testing and pathology terms for informational purposes only and does not constitute medical advice. Your dermatologist and pathologist should interpret your results and decide whether additional testing is needed.