Case Presentation: We present a case of a 27-year-old male with no significant past medical history who presented with a three week history of fever, sore throat, persistent non-productive cough, arthralgia, myalgia, as well as a diffuse body rash.A month prior to this presentation, he had seen his primary provider for a lump that he noticed under his left axilla for which he was prescribed a course of antibiotics. In the interim, he had presented to an Urgent Care, where he was started on prednisone which improved the arthralgia and skin rash but they returned on stopping the treatment.
His major complaints on presentation were his upper extremity arthralgia and diffuse rash. He denied any sexual activity within the last year, genitourinary complaints, change in appetite, weight, recent travel, or exposures including insect or tick bites.
On exam, he was febrile to 39.2 C and had a diffuse, blanching, maculopapular rash on his trunk and extremities but sparing the palms and soles. He also had asymmetric polyarthritis of upper extremities including wrists, hands, and elbows. He had a leukocytosis of 14,500, with a left shift but further workup revealed normal complement levels, urinalysis, negative viral serologies including viral hepatitis, EBV, Measles, CMV, herpes and HIV, rapid streptococcal test, and normal plain chest film, making infectious etiology less likely. Initial inflammatory markers, including ESR and CRP, were elevated and hence he was empirically started on steroids. Serum and urine proteins were found to be within limits, chlamydia-gonococcus negative, blood cultures along with syphilis, Bartonella, and Lyme serologies remained negative and transthoracic echocardiogram did not reveal vegetations. His Ferritin was found elevated at 535 but deemed not elevated enough to suspect Adult onset Still’s Disease.
CT thorax revealed left axillary lymphadenopathy measuring 3.7 cm by 2.2 cm while that of the abdomen showed hepatosplenomegaly. The axillary node was biopsied with a fine needle and revealed lymphoid hyperplasia but was negative for lymphoma or other cellular atypia. At this point he was a diagnostic challenge as he was a case of fever of unknown origin with a picture resembling lymphoma/leukemia, any number of rheumatologic pathologies, but without objective evidence towards any of them and continued fever and generalized malaise.
He then underwent excisional biopsy of the lymph node, which revealed reactive follicular hyperplasia with progressive transformation of germinal centers and Castleman changes. He has eventually been referred to hematology for further outpatient management.

Discussion: Unicentric Catleman’s disease (UCD) is one of the rarest hematological disorders with no reliable population estimates. It is primarily a disease of the lymph nodes seen in infection with herpesviridae or other forms of immunodeficiency including HIV. A high index of suspicion is required in an otherwise unexplained constellation of symptoms to manage patients in a timely fashion. Our first consideration of the diagnosis was at the time of pathology confirmation.

Conclusions: Outcomes have been found to differ in surgical versus non-surgical management of UCD and significant mortality has been demonstrated in patients in whom surgical excision was not done. Management is hence time sensitive and it is important to consider a wider set of differential diagnoses when it comes to atypical presentations, young population with no special predisposition, non-response to first line treatment, etc.