<PAGE>
 
                              TWO WISCONSIN CIRCLE


                         ADDENDUM NO. 6 TO OFFICE LEASE
                         ------------------------------


          THIS ADDENDUM NO. 6 TO OFFICE LEASE (this "Addendum") is made and
entered into this __ day of July, 1998, by and between TWO WISCONSIN CIRCLE
JOINT VENTURE, a Maryland joint venture, hereinafter called "Lessor," and
HEALTHCARE FINANCIAL PARTNERS, INC., formerly known as Health Partners Financial
Corporation, a Delaware corporation, hereinafter called "Lessee."


                                   WITNESSETH:
                                   -----------

          WHEREAS, by Office Lease dated the 4th day of January 1996, as amended
by Addendum No. 1 to Office Lease dated the 26th day of July 1996, Addendum No.
2 to Office Lease dated the 13th day of August 1996, Addendum No. 3 to Office
Lease dated the 17th day of July 1997, Addendum No." 4 to Office Lease dated the
27th day of February, 1998 and Addendum No. 5 to Office Lease also dated the
27th day of February, 1998 (as so amended, the "Lease"), Lessor currently leases
to Lessee approximately 21,820 square feet of rentable area on the fourth (4th)
floor (the "Existing Demised Premises"), in the building situated at Two
Wisconsin Circle, Chevy Chase, Maryland (the "Building"); and

          WHEREAS, Lessor and Lessee desire to expand the Existing Demised
Premises by adding thereto and incorporating therein, on a month-to-month basis
upon the terms and conditions hereinafter set forth. additional space on the
eighth (8th) floor of the Building comprising approximately 2,201 square feet of
rentable area (the "Additional Space").

          NOW, THEREFORE, in consideration of the mutual covenants and
agreements hereinafter set forth, the parties hereto do mutually agree that the
Lease shall be and is hereby amended to provide as follows, all capitalized
terms being as defined in the Lease unless otherwise noted herein:


1. ADDITIONAL SPACE
   ----------------

          There is hereby added to the Existing Demised Premises, and Lessor
does hereby lease to Lessee, and Lessee does hereby lease from Lessor, the
Additional Space, on a month-to-month basis and otherwise subject to and upon
all of the terms and conditions of the Lease, as amended hereby, to the end that
the Demised Premises under the Lease shall be the said approximately 21,820
square feet of rentable area on the fourth (4th) floor of the Building, as well
as 2,201 square feet of rentable area on the eighth (8th) floor of the Building,
as such eighth (8th) floor space is outlined on the floor plan attached hereto
and made a part hereof as Exhibit A.
<PAGE>
 
2.  TERM
    ----

    (A) The Additional Space shall be added to the Existing Demised Premises
on the Addition Date, which shall be the 24th day of July, 1998 (the
"Anticipated Addition Date"), or such later date as may be established pursuant
to the provisions below in this Section 2, and the term of the Lease as to the
Additional Space only shall thereafter continue on a month-to-month basis. It is
expressly understood and agreed that the term of the Lease as to the Existing
Demised Premises shall remain unaffected. Lessee shall give to Lessor at least
thirty (30) days' written notice of its intention to quit the Additional Space,
and Lessee shall be entitled to at least thirty (30) days' written notice from
Lessor to quit the Additional Space, unless Lessee is in default under the
Lease, as hereby amended, in which event Lessee shall not be entitled to any
notice to quit, the usual thirty (30) days' notice to quit being hereby
expressly waived, From and after the Addition Date and continuing for so long as
the month-to-month tenancy on the Additional Space shall continue, the
Additional Space shall be deemed to be part of the premises demised under the
Lease for all purposes, and the term "Demised Premises" as used throughout the
Lease shall be construed to include both the Existing Premises and the
Additional Space.

    (B) It is understood and agreed that the obligations of Lessor and
Lessee under this Addendum are contingent upon the existing tenant of the
Additional Space vacating and surrendering full possession of the same on or
about July 15, 1998. In the event Lessor is unable to deliver possession of the
Additional Space on the Anticipated Addition Date, because the existing tenant
has failed to so vacate, Lessor shall not be liable or responsible for any
claims, damages or liability arising in connection therewith or by reason
thereof, nor shall Lessee be excused or released from the Lease, as amended
hereby, because of Lessor's inability to deliver possession of the Additional
Space on that date. The Addition Date, however, shall be extended to the earlier
of (i) the date the Additional Space is occupied by Lessee or (ii) the date
which is ten (10) days after the date Lessor has notified Lessee in writing that
the existing tenant has vacated the Additional Space and possession thereof is
available to Lessee; provided. however, that if the existing tenant fails to
vacate and surrender full possession of the Additional Space on or before August
31, 1998, then either Lessor or Lessee shall have the right to cancel and
terminate this Addendum without further liability by giving written notice of
such cancellation and termination to the other on or before September 15, 1998,
and this Addendum shall be null and void and of no further force or effect upon
the delivery of such notice. Lessor shall endeavor to keep Lessee informed as to
the status of its efforts to recapture possession of the Additional Space from
the existing tenant. When Lessee accepts possession of the Additional Space,
Lessor and Lessee shall execute the "Declaration as to Date of Delivery and
Acceptance of Possession of Premises," attached hereto as Exhibit B, which shall
specify the Addition Date.


3.  RENT
    ----

    The additional monthly rent for the Additional Space (hereinafter
referred to as "Additional Monthly Rent"), which Lessee hereby agrees to pay in
advance to Lessor and Lessor hereby agrees to accept, shall be the sum of Five
Thousand Three Hundred Nineteen and 08/100ths Dollars ($5,319.08).

                                      -2-
<PAGE>
 
    If the Addition Date is a date other than the first day of a calendar
month, the Additional Monthly Rent from such date until the first day of the
following calendar month shall be prorated at the rate of one-thirtieth (1/30th)
of the Additional Monthly Rent for each day, payable in advance. Additional
Monthly Rent as specified above shall be payable as additional rent under the
Lease, as amended hereby, simultaneously with each payment of Monthly Rent in
advance on the first day of each calendar month during the month-to-month
tenancy on the Additional Space.

    Effective on each anniversary of the Addition Date, if Lessee is then
in occupancy of the Additional Space (it being understood and agreed that
nothing in this paragraph shall alter, modify or affect the month-to-month
tenancy as to the Additional Space), the Additional Monthly Rent shall be
increased by adding thereto One Hundred Eighty-Three Dollars and 42/ lOOths
Dollars ($183.42). For example, on the first (1st) anniversary of the Addition
Date, the Additional Monthly Rent shall be increased to Five Thousand Five
Hundred Two and 50/100ths Dollars ($5,502.50), on the second (2nd) anniversary
of the Addition Date, the Additional Monthly Rent shall be increased to Five
Thousand Six Hundred Eighty-Five and 92/100ths Dollars ($5,685.92), and so
forth.


4.  PRE-OCCUPANCY TENANT WORK
    -------------------------

    The Additional Space has been previously occupied, and it is acknowledged
that Lessor has heretofore completed tenant work within the Additional Space
substantially in accordance with the provisions of Exhibit B of the Lease.
Lessee shall accept the Additional Space "as is" upon the Addition Date;
provided, however, that Lessor shall repaint the Additional Space at its expense
prior to the Addition Date in accordance with the "Painting" specification set
forth in Exhibit B to the Lease, Any tenant work and installations desired by
Lessee for its occupancy of the Additional Space shall be undertaken by Lessee
at its cost and expense pursuant to Section 9 of the Lease.


5.  LEASE PROVISIONS APPLICABLE
    ---------------------------

    Subject to the month-to-month tenancy on the Additional Space, all of the
terms and conditions of the Lease, as amended or supplemented hereby, shall be
applicable to the Additional Space hereby added to the Existing Demised
Premises. All terms and conditions of the Lease, as amended or supplemented
hereby, are hereby ratified and affirmed and shall remain in full force and
effect.




                   (Signatures appear on the following pages)

                                      -3-
<PAGE>
 
    IN WITNESS WHEREOF, Lessor and Lessee have caused this Addendum to be
signed in their names by their duly authorized representatives and delivered as
their act and deed, intending to be legally bound by its terms and provisions.


                                LESSOR:

                                TWO WISCONSIN CIRCLE JOINT VENTURE,
                                a Maryland joint venture

Attest:                         By: The Chevy Chase Land Company of 
                                    Montgomery County, Maryland, a General
                                    Partner



/s/ David G. Dolan                  By: /s/ Gavin M. Farr
---------------------------            ----------------------------------
Vice President                         Name: Gavin  M. Farr
(SEAL)                                 Title: Chairman


STATE OF MARYLAND
COUNTY OF MONTGOMERY, ss:


    I, Ellen M. Gott, a Notary Public in and for the State of Maryland, do
hereby certify that Gavin M. Farr, who is personally well known to me as the
person who executed the foregoing and annexed Addendum, dated the 17th day of
July, 1998, on behalf of the Lessor, to acknowledge the same, personally
appeared before me in said jurisdiction and acknowledged said Addendum to be the
act and deed of The Chevy Chase Land Company of Montgomery County, Maryland, as
a general partner of and for and on behalf of the Lessor, and delivered the same
as such.

    GIVEN under my hand and seal this 17th day of July, 1998.


                                /s/ Ellen M. Gott
                                ------------------------------
                                Notary Public
My Commission Expires
                                                      ELLEN M. GOTT
                                             NOTARY PUBLIC STATE OF MARYLAND
                                             My Commission Expires July 21, 2001

                                      -4-
<PAGE>
 
                                     LESSEE:

                                     HEALTHCARE FINANCIAL PARTNERS, INC.,
                                     a Delaware corporation
Attest:



[ILLEGIBLE SIGNATURE]                By: /s/ Edward P. Nordberg, Jr.
-----------------------------           --------------------------------
Secretary                               Name: Edward P. Nordberg, Jr.
(SEAL)                                  Title: EVP
                                     
                                     
                                     
STATE OF MARYLAND
COUNTY OF MONTGOMERY, ss:

     I, Christa D. Dale, a Notary Public in and for the State of Maryland, do
hereby certify that Edward P. Nordberg, Jr., who is personally well known to me
as the person who executed the foregoing and annexed Addendum, dated the 17 day
of July, 1998, on behalf of the Lessee, to acknowledge the same, personally
appeared before me in said jurisdiction and acknowledged said Addendum to be the
act and deed of Healthcare Financial Partners, Inc. and delivered the same as
such.

     GIVEN under my hand and seal this 17 day of July, 1998.


                                  /s/ Christa D. Dale
                                  ---------------------------------
                                  Notary Public

My Commission Expires

Christa D. Dale, Notary Public
     Montgomery County
     State of Maryland
My Commission Expires Feb. 13, 1999

                                      -5-
<PAGE>
 
                              TWO WISCONSIN CIRCLE

                                   EXHIBIT "B"

                     DECLARATION AS TO DATE OF DELIVERY AND
                      ACCEPTANCE OF POSSESSION OF PREMISES


          Attached to and made a part of the Addendum, dated the _____ day of
July, 1998, entered into by and between Two Wisconsin Circle Joint Venture, as
Lessor, and Healthcare Financial Partners, Inc., as Lessee.

          Lessor and Lessee do hereby declare and evidence that possession of
the Additional Space was accepted by Lessee on the ________ day of________,
1998. The Addendum is now in full force and effect. For the purpose of the
Addendum, the Addition Date is established as being on the said date.


LESSEE:                              LESSOR:

HEALTHCARE FINANCIAL                 TWO WISCONSIN CIRCLE JOINT VENTURE
PARTNERS, INC.
                                     By: The Chevy Chase Land Company of
                                         Montgomery County, Maryland

By:                                      By:
   ---------------------------              --------------------------- 
   Name:                                    Name:
   Title:                                   Title:

                                      -6-