Cryptococcus neoformans Case File

Cryptococcus neoformans Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 42

A 32-year-old man with known AIDS is brought to the emergency room with headache and fever for the past 3 days. According to family members who are with him, he has been confused, forgetful, and irritable for a few weeks prior to the onset of these symptoms. They state that he has advanced AIDS with a low CD4 count and has had bouts of pneumocystis pneumonia, candidal esophagitis, and Kaposi sarcoma. He is on multiple medications, although they don’t know whether he is actually taking them. On examination, he is cachetic and frail appearing. He is confused and only oriented to his name. His temperature is 37.8°C (100°F), and his other vital signs are normal. Examination of his cranial nerves is normal. He has minimal nuchal rigidity. Cardiovascular, pulmonary, and abdominal examinations are normal. He is hyperreflexic. A head CT scan is normal. A report of the microscopic examination of his cerebrospinal fluid obtained by lumbar puncture comes back from the laboratory and states that there were numerous white blood cells, predominantly lymphocytes, and no organisms identified on Gram stain but a positive India ink test.

◆ What organism is the likely cause of this illness?

◆ What characteristic of this organism is primarily responsible for its virulence?

ANSWERS TO CASE 42: Cryptococcus neoformans

Summary: A 32-year-old male with advanced AIDS presents with meningitis. The India ink test is positive.

◆ Most likely etiology for this man’s meningitis: Cryptococcus neoformans.

◆ Characteristic of this organism is primarily responsible for its virulence: Cryptococcus neoformans is known characteristically to produce a mucopolysaccharide capsule. This is a key feature of this organism’s virulence, because it is antiphagocytic and also interferes with leukocyte migration to sites of infection.

CLINICAL CORRELATION

Cryptococcus neoformans is an encapsulated monomorphic fungi that commonly causes chronic meningitis in immune-suppressed individuals and occasionally in immune-competent persons. The lungs are the primary site of infection, although the organism appears to have specific affinity for the brain and meninges on systemic spread. Cryptococcus neoformans is the leading cause of fungal meningitis and is an important cause of mortality in AIDS patients.

APPROACH TO SUSPECTED Cryptococcus neoformans INFECTION

Objectives

1. Be familiar with the characteristics and disease presentation of C. neoformans fungi.
2. Know the methods of diagnosis of infection with C. neoformans.
3. Be able to describe the treatment and prevention of infection.

Definitions

Meningitis: Inflammation of the meninges.

Nuchal rigidity: Stiffness of the neck associated with meningitis.

Cachetic: Weight loss or wasting because of disease or illness.

DISCUSSION

Characteristics of Cryptococcus neoformans That Impact Transmission

Cryptococcus neoformans is an encapsulated yeast, 4–6 mm in diameter, which is distributed globally. The most common serotypes are found in high concentrations in pigeon and other bird droppings, although they do not appear to cause disease in these hosts. The most common route of transmission to humans is via aerosolization of the organism followed by inhalation into the lungs. Direct animal-to-person transmission has not been shown. Unlike other systemic fungi, C. neoformans is monomorphic, not dimorphic, and grows as budding yeast cells at both 25°C (77°F) in culture and at 37°C (98.6°F) in tissues. When grown in culture, C. neoformans produces white- or tan-colored mucoid colonies in 2–3 days on a variety of common fungal media. Microscopically, the organism appears as spherical budding yeast, surrounded by a thick capsule. Cryptococcus neoformans differs from the other nonpathogenic cryptococcal strains by its ability to produce phenol oxidase and growth at 37°C (98.6°F).

The capsule is an important virulence factor of Cryptococcus, and it consists of long, unbranched polysaccharide polymers. Capsule production is normally repressed in environmental settings and is stimulated by physiologic conditions in the body. The capsule is antiphagocytic, because of its large size and structure and has also been shown to interfere with antigen presentation and the development of T-cell-mediated immune responses at sites of infection. This suppression of an immune response can allow for multiplication of the organism and promotion of its spread outside the respiratory tract. Once outside the lung, the organism appears to have an affinity for the central nervous system (CNS), possibly because of its ability to bind C3 and the low levels of complement found in the CNS.

Diagnosis

Inhalation of these aerosolized yeast cells leads to a primary pulmonary infection. The infection may be asymptomatic or may result in a flu-like respiratory illness or pneumonia. Commonly, cryptococcal pulmonary infection is identified only as an incidental finding on a chest x-ray being performed for other reasons. Often the infection and resulting lesions appear suspicious for a malignancy, only to be diagnosed properly after surgical removal. The most commonly diagnosed cryptococcal disease is meningitis, which results from hematogenous spread of the organism from the lung to the meninges. It occurs most commonly in persons with AIDS or those who are immunosuppressed for other reasons, but it can occasionally occur in persons without underlying conditions. Outside the lungs, C. neoformans appears to have a preference for the cerebrospinal fluid (CSF), but disseminated disease can also cause infections of the skin, eye, and bone. Cryptococcal meningitis may be insidious in its onset, slowly causing mental status changes, irritability, or confusion that occurs over weeks to months, or it can occur acutely, with immediate changes in mentation and meningeal symptoms. Clinical disease may present with intermittent headache, irritability, dizziness, and difficulty with complex cerebral functions and may even be mistaken as psychoses. Seizures, cranial nerve signs, and papilledema may appear in late clinical course.

A diagnosis of C. neoformans infection is made primarily by clinical presentation and examination of CSF for increased pressure, increased number of white cells, and low glucose levels. Serum and CSF specimens should also be tested for polysaccharide capsular antigen by latex agglutination or enzyme immunoassay. Another classic test for C. neoformans is the India ink test, which is an easy and rapid test that is positive in approximately 50 percent of patients with cryptococcal disease. A drop of India ink is placed on a glass slide and mixed with a loopful of CSF sediment or a small amount of isolated yeast cells. A cover slip is added and the slide is examined microscopically for encapsulated yeast cells that exclude the ink particles.

Treatment and Prevention

Cryptococcus neoformans infections can be treated with antifungal agents such as amphotericin B or fluconazole. Amphotericin B is a broad-spectrum chemo-therapeutic agent and is the most effective drug for severe systemic mycoses. However, it is an extremely nephrotoxic agent to which all patients have adverse reactions such as fever, chills, dyspnea, hypotension, and nausea. Fluconazole is less toxic than amphotericin B and produces fewer side effects; however, resistance to fluconazole has been shown to occur. AIDS patients with cryptococcosis are required to continue lifelong suppressive therapy with fluconazole to prevent relapse of fungal infection.

COMPREHENSION QUESTIONS

[42.1] A 32-year-old man who lives in downtown Philadelphia presents to his physician with a 4-day history of terrible headache, fever, and stiff neck. He has always been in good health and attributes this to his healthy eating habits and his daily running through the city parks near his apartment. The physician suspects the man may have cryptococcal meningitis and collects CSF for examination. Which of the following results would you most likely expect from this patient’s CSF studies?

A. Elevated CSF pressure with increased white cell counts

B. Elevated polymorphonuclear cells with high protein levels

C. Elevated lymphocytes with normal glucose levels

D. Normal CSF pressure with a positive Gram stain reaction

E. Normal CSF pressure with negative Gram stain reaction

[42.2] Which of the following laboratory tests would best definitely diagnose cryptococcal infection in the above patient?

A. Quelling reaction capsular swelling

B. Latex agglutination test for polysaccharide capsular antigen

C. Ouchterlony test for fungal infection

D. India ink test for the presence of capsulated yeast

E. Gram stain reaction

[42.3] A 35-year-old man with AIDS presents to the local clinic with complaints of nausea, vomiting, confusion, fever and staggering gait. A lumbar puncture is performed, and an organism with a halo is noted with India ink preparation. What drug would be most beneficial?

A. Ketoconazole and amphotericin B

B. Fluconazole and amphotericin B

C. Nystatin and ketoconazole

D. Nystatin and miconazole

E. Griseofulvin

[42.4] A 34-year-old white homeless man in New York city is brought in by the police to the emergency room because he was found wandering the streets confused with a staggering gait. On physical exam, he is noted to have acne like lesions over a large part of his body accompanied with skin ulcers. He is febrile and has some cranial nerve deficits. A short time later the man becomes short of breath, which was determined to be caused by severe cerebral edema compressing the medulla. Which of the following is the most likely causative agent?

A. Histoplasma capsulatum

B. Coccidioides immitis

C. Exophiala werneckii

D. Sporothrix schenckii

E. Cryptococcus neoformans

Answers

[42.1] A. Meningitis caused by C. neoformans infection typically results in increased CSF pressure with an increased number of white cells and low glucose levels; answers B, C, D, and E are incorrect: both (B) and (D) appropriately describe meningitis caused by a bacterial agent such as Neisseria meningitides; (C) appropriately describes meningitis caused by a viral agent such as herpes simplex virus; (E) describes normal CSF findings.

[42.2] B. answers A, C, D, and E are incorrect: (A) is a test useful for diagnosing Streptococcus pneumoniae and uses capsule-specific antibody to cause capsule swelling; (C) is an immunodiffusion test useful in diagnosing Histoplasma and Blastomyces fungal infections; (D) does provide rapid diagnosis of Cryptococcus neoformans; however, this assay is positive in only 50 percent of cryptococcal cases; (E) the Gram stain is more useful in diagnosing bacterial infections, because it would show the presence of yeast cells, but the capsule would not be visible.

[42.3] B. The organism present is C. neoformans, the usual treatment for cryptococcosis is amphotericin B and fluconazole. The other drugs listed are not indicated for cryptococcosis. Ketoconazole is usually used for chronic mucocutaneous candidiasis. Nystatin is used for candidiasis, and griseofulvin is indicated for dermatophytes of the hair, skin, and nails. Miconazole is used for topical fungal infections, oral thrush, and vaginitis.

[42.4] E. The symptoms described including acne-like lesions, skin ulcers, fever, confusion, staggering gait and cranial nerve deficits are a classic example of Cryptococcus neoformans infection. In some patients the cerebral edema progresses to a fatal stage compressing the medulla reducing respiratory efforts. The other yeast listed do not cause cerebral edema. Exophiala werneckii causes tinea nigra characterized by dark patches on the hands and soles of the feet. Sporothrix schenckii is usually associated with a prick from a rose thorn. Coccidioides immitis is associated with the desert southwest. Histoplasma capsulatum is usually associated with a Mississippi river valley history, as well as lesions that calcify.

MICROBIOLOGY PEARLS ❖ Cryptococcus neoformans is transmitted via aerosolized pigeon or bird droppings. ❖ Clinical manifestations: headache, altered mental state, nuchal rigidity, often associated with AIDS. ❖ Identification: clinical symptoms, examination of CSF for increased pressure and number of white cells with low glucose levels, and a positive capsular antigen latex agglutination and India ink tests. ❖ Current treatment: amphotericin B or fluconazole.

REFERENCES

Brooks GF, Butel JS, Morse SA. Jawetz, Melnick, & Adelberg’s Medical Microbiology, 23rd ed. New York: McGraw-Hill, 2004:647–9. 

Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology, 5th ed. St. Louis,MO: Mosby, 2005:779–800. 

Ryan JR, Ray CG. Sherris Medical Microbiology, 4th ed. New York: McGraw-Hill, 2004:647–9.

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