<PAGE>
 
                             TWO WISCONSIN CIRCLE

                        ADDENDUM NO. 4 TO OFFICE LEASE
                        ------------------------------


          THIS ADDENDUM NO. 4 TO OFFICE LEASE (this "Addendum") is made and
entered into this 27th day of February, 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, and Addendum No. 3 to
Office Lease dated the 17th day of July 1997 (as so amended, the "Lease7"),
Lessor currently leases to Lessee approximately 15,577 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, upon the terms and
conditions hereinafter set forth, additional space on the fourth (4th) floor of
the Building comprising approximately 1,116 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, 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 approximately 16,693 square feet of rentable area on the fourth (4th)
floor of the Building, as outlined on the floor plan attached hereto and made a
part hereof as Exhibit A.


2.        TERM
          ----

          (A) The Additional Space shall be added to the Existing Demised
Premises on the Addition Date, which shall be the 1st day of April, 1998 (the
"Anticipated Addition Date"), or such later date as may be established pursuant
to the provisions below in this Section 2. The term of the Lease as to the
Additional Space shall expire on the same date as the term of the
<PAGE>
 
Lease as to the Existing Demised Premises so as to be coterminous for all
purposes with the term of the Lease as to the Existing Demised Premises.

          (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 March 31, 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 May
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 June 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 as follows:

          Lease Period                                 Additional Monthly Rent
          ------------                                 -----------------------

          From the Addition Date through
          the twelfth (12th) full calendar
          month thereafter                                     $2,790.00

          From the thirteenth (13th) full calendar 
          month through the twenty-fourth (24th)
          full calendar month                                  $2,883.00

          From the twenty-fifth (25th) 
          full calendar month through the 
          thirty-sixth (36th)
          full calendar month thereafter                       $2,976.00

                                      -2-
<PAGE>
 
          From the thirty-seventh (37th) 
          full calendar Month through the
          forty-eighth (48th)
          full calendar month                                  $3,069.00

          From the forty-ninth (49th) 
          full calendar Month through 
          the expiration of the
          initial term of the Lease                            $3,162.00


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 term of the Lease.


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, and Lessor shall have no obligation to furnish or install any items
whatsoever of tenant work within the Additional Space. All 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.        ADDITIONAL DEPOSIT
          ------------------

          Lessor currently holds the sum of Forty-Five Thousand Four Hundred
Thirty-Two and 92/100 Dollars ($45,432.92) as a non-interest bearing cash
security deposit under the Lease. Upon the Addition Date and as a condition to
delivery of possession of the Additional Space, Lessee shall deposit with Lessor
the additional sum of Three Thousand One Hundred Sixty-Two and 00/ 100 Dollars
($3,162.00). The resulting sum in the amount of Forty-Eight Thousand Five
Hundred Ninety Four 92/100 Dollars ($48 594.92) shall continue to be held by
Lessor as a non-interest bearing cash security deposit under the Lease, as
amended hereby, pursuant to and in accordance with the provisions of Section 6
of the Lease. If Lessor elects to apply all or any portion of the increased cash
deposit to cure Lessee's default, Lessee shall be obligated to promptly deposit
with Lessor cash in an amount sufficient to restore the cash security deposit to
Forty-Eight Thousand Five Hundred Ninety Four and 92/100 Dollars ($48,594.92).


6.        LEASE PROVISIONS APPLICABLE
          ---------------------------

          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. Once

                                      -3-
<PAGE>
 
added to the Existing Demised Premises, the Additional Space shall be deemed to
be a part of the premises demised under the Lease for all purposes. 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.

          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

                                   
[SIGNATURE APPEARS HERE]           By:  /s/ Edward Hall Asher
------------------------                ---------------------------------
    VICE PRESIDENT                      Name:  Edward Hall Asher
[SEAL APPEARS HERE]                     Title: President
                                        


STATE OF MARYLAND
COUNTY OF MONTGOMERY, ss:

          I, Donna Geraci, a Notary Public in and for the State of Maryland, do
hereby certify that Edward Hall Asher, who is personally well known to me as the
person who executed the foregoing and annexed Addendum, dated the 27 day of
Feb., 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 9th day of March, 1998.


                                         /s/  Donna Geraci
                                         ---------------------------
                                         Notary Public

My Commission Expires  5/19/99


                   (Signatures Continue on the Following Page)

                                      -4-
<PAGE>
 
                                      LESSEE:

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

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

       I, Sue E. Murray, 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 27th
day of February, 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 9th day of March, 1998.

                                   /s/ Sue E. Murray         
                                  -------------------------------------  
                                  Notary Public
                                  Sue E. Murray
My Commission Expires 8/7/01      

                                      -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
January, 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-