Pneumocystis Carinii Pneumonia (PCP)

Pneumocystis carinii (NEW-mo-SIS-tis CA-RIN- nee-eye) pneumonia, or "PCP," is a severe illness found in people with HIV. It is caused by a germ called Pneumocystis carinii. Most people infected with this germ don't get pneumonia because their immune systems are normal. People whose immune systems are badly damaged by HIV can get PCP. People with HIV are less likely to get PCP today than in earlier years. However, PCP is still the most common serious infection among people with AIDS in the United States.

Causes

P.carinii, the cause of PCP, usually is classified as a protozoan, although some investigators consider it more closely related to fungi. The organism exists as a saprophyte in the lungs of humans and various animals.P.carinii is part of the normal flora in most healthy people but becomes an aggressive pathogen in the immunocompromised patient. Impaired cell­mediated (T-cell) immunity is thought to be more important than impaired humoral (B-cell) immunity in predisposing the patient to PCP, but the immune defects involved are poorly understood.

The primary transmission route seems to be air, although the organism already resides in most people. The incubation period probably lasts for 4 to 8 weeks. Impaired cellular immunity is the major factor that predisposes a person to pneumocytosis. Defects in B-cell function also play a role.

The organism invades the lungs bilaterally and multiplies extracellularly. As the infestation grows, alveoli fill with organisms and exudate, impairing gas exchange. The alveoli hypertrophy and thicken progressively, eventually leading to extensive consolidatian.

Signs and symptoms

• fever
• cough -- often mild and dry
• shortness of breath -- especially with exertion (activity)
• rapid breathing

Diagnostic tests 

Histologic studies can confirm P.carinii. In many patients with HIV, initial examination of a first-morning sputum specimen (induced by inhaling an ultrasonically dispersed saline mist) may be sufficient. This technique usually is ineffective in patients without HIV. 

In all patients, fiberoptic bronchoscopy remains the most commonly used diagnostic tool to confirm PCP. Invasive procedures, such as transbronchial biopsy and open lung biopsy, are less commonly used.

In addition, a chest X-ray may show slowly progressing, fluffy infiltrates and occasional nodular lesions or a spontaneous pneumothorax. These findings must be differentiated from findings in other types of pneumonia or adult respiratory distress syndrome.

Treatment

The drug of choice for all types of PCP is trimethoprim-sulfamethoxazole (TMP-SMZ) administered orally or I.V. Adverse reactions include fever, rash, neutropenia, thrombocytopenia, hepatitis, and hyperkalemia.

Pentamidine may be administered slowly I.V. in a single dose of 4 mg/kg/day; it is as effective as TMP-SMZ but is toxic for almost all recipients. Adverse effects include hypotension, cardiac arrhythmia, hyperglycemia or hypoglycemia, azotemia, electrolyte changes, and neutropenia. Other regimens are also prescribed for patients who don't tolerate either of these medications.

Supportive measures, such as oxygen therapy, mechanical ventilation, adequate nutrition, and fluid balance, are important adjunctive therapies. Oral morphine sulfate solution may reduce respiratory rate and anxiety, enhancing oxygenation.

Prevention

Preventive therapy is recommended for AIDS patients, for individuals on chronic high dose corticosteroids, as well as individuals with previous episodes of PCP. AIDS patients with CD4 counts below 200 should receive prophylactic (preventive) therapy.

While the most effective preventive drug is trimethoprim-sulfamethoxazole, other options include dapsone, atovaquone, and aerosolized pentamidine.