• Time to improvement [ Time Frame: 14 days ] [ Designated as safety issue: No ]
• One-log reduction in HHV-8 peripheral blood viral load [ Time Frame: 14 days ] [ Designated as safety issue: No ]

• Time to improvement
• One-log reduction in HHV-8 peripheral blood viral load

• Safety and tolerability of valganciclovir [ Time Frame: 14 days ] [ Designated as safety issue: Yes ]
• Proportion of patients resolving symptoms by 4 days [ Time Frame: 14 days ] [ Designated as safety issue: No ]
• HHV-8 detection in the plasma or oropharynx [ Time Frame: 14 days ] [ Designated as safety issue: No ]

• Safety and tolerability of valganciclovir
• Proportion of patients resolving symptoms by 4 days
• HHV-8 detection in the plasma or oropharynx

The purpose of the study is to learn whether people who are experiencing an MCD (multicentric Castleman's Disease) flare will improve after taking valganciclovir. MCD is a type of inflammatory disease associated with Human Herpesvirus 8 (HHV-8). Valganciclovir is FDA approved for treating a different type of Human Herpesvirus, but not approved for the treatment of HHV-8. It is therefore considered experimental in this study.

All participants will undergo an initial screening appointment. At this visit, participants will be tested for Human Herpesvirus 8 (HHV-8), the virus that is associated with MCD, and we will review participants' medical history and medical records to determine whether he/she has MCD. If participants do not live within the Seattle area, this visit may occur over the phone.

Those who qualify for the study will be followed for up to 2 years. During that 2 year period, participants will be asked to collect oral swabs once a week and have blood drawn monthly. If subjects do not live within the Seattle-area, they will be asked to ship these samples to UW for testing. We will provide subjects with instructions for these shipments. This will be done at no cost to the participant.

If during the 2 year period the participant experiences a MCD flare, he/she will be admitted to the University of Washington Medical Center's Clinic Research Center for 14-days. If the participant does not live within the Seattle-area, all travel expenses will be covered.

The study will enroll a total of 8 patients who will receive open-label valganciclovir for 14-days. Everyday during the hospitalization, participants will have blood drawn (to check your HHV-8 levels), 1 oral swab will be collected and a general physical exam will be performed.

Inclusion Criteria:

• Age 18 years
• Negative pregnancy test (for female participants)
• Diagnosis of MCD for over one year, with a history of at least one MCD recurrence annually
• Evidence of infection with HHV-8
• A willingness to travel and reside temporarily in Seattle for completion of the study protocol.
• For HIV-infected participants, a stable antiretroviral regimen for the past 6 months

Exclusion Criteria:

• Concurrent Kaposi sarcoma or non-hodgkin's lymphoma
• A history or evidence of CMV disease
• Hypersensitivity to ganciclovir or valganciclovir
• Use of high-dose acyclovir (>800 mg bid), valacyclovir (>1000 mg qd) or famciclovir (>1000 mg qd), ganciclovir, foscarnet, or cidofovir
• Neutropenia (ANC <1500)
• Renal insufficiency with serum creatinine > 1.5 mg/ml or CrCl < 60
• AST or ALT > 5 times upper limit of normal
• Concurrent administration of medications which are often associated with severe neutropenia or thrombocytopenia (i.e., chemotherapy, etc)
• Concurrent administration of probenecid or didanosine.
• Inability to read and understand English