Epidemiology Degree

It is now known that cat scratch disease (CSD) is a multisystem diseasecaused by a small Gram negative bacillus named Bartonella henselae, formerlyknown as Rochalimaea henselae. As early as 1932, physicians in the UnitedStates recognized patients with CSD, but the cause of the disease eludeddetection until 1983 when researchers at the Armed Forces Institute ofPathology at Walter Reed Army Medical Center in Washington, D.C. detected theorganism in lymph node tissue from patients with clinical CSD. Identificationof the causative organism has allowed researchers to identify the epidemiologyand transmission of the disease, identify atypical forms of CSD, developserologic diagnostic tests, and perform placebo-controlled treatmenttrials.

A four year old girl presents to the pediatric clinic with a chief complaintof a slowly enlarging mass in her right armpit for the past two weeks. She hashad no fever, but has had some loss of appetite. The mass was initially smalland did not hurt; however, it has now grown to the size of an orange and hasbecome painful. She cannot lower her arm due to the pain from the mass, and shecarries her arm extended at 90 degrees to her body.

Movement of her arm exacerbates the pain. She does have a 3 month old kittenat home that she “rescued from a sewer”. It was covered with fleas when shefound it. It playfully bites and scratches her. Three weeks ago it scratchedher right thumb. The scratch healed, but a small “wart” has developed in theline of the scratch. There is a scab on the wart and her mother has tried tosqueeze the wart, but no pus has come out.

ROS: Non-contributory. No cough. No weight loss. No change in activity otherthan being unable to use her right arm well.Exam: VS T 37.2, RR 18, P 102, BP100/60. She is alert and very cooperative. HEENT is negative. Neck is supplewithout adenopathy. Chest is clear. Heart regular without murmur. Abdomen examis normal without hepatosplenomegaly. Neurologic exam is normal (mental status,gait, strength, and reflexes). Her right axilla reveals an 8×8 cm firm, tender,mobile, warm, non-erythematous, non-fluctuant mass that is consistent with anenlarged axillary lymph node. Her right thumb has a 1 cm linear, non-inflamed,healing scar that is consistent with a kitten scratch. In the middle of thelinear scar, there is a 3 mm brownish-red papule with a small centralcrust.

Lab: CBC WBC 8.0, 62% segs, 10% bands. Ultrasonography of the mass revealsthat it is a matted group of about 5 lymph nodes which are mostly solid inappearance. There is evidence of a small amount of necrosis at the periphery ofone of the lymph nodes.

Impression: Lymphadenopathy due to cat scratch disease.

Clinical course: Because the axillary node is enlarged and painful, youelect to treat her with oral azithromycin at a dose of 10 mg/kg/day for thefirst day and 5 mg/kg/day for the next 4 days. Serology for Bartonella henselaeis obtained, and the result returns one week later with an IgG of 1:512 (apositive result is a value greater than 1:64). The node remains the same sizefor a week and then begins to get smaller. The adenopathy resolves in onemonth.