•Whipple’s disease should be considered as a differential diagnosis to sarcoidosis.•PCR testing of duodenal specimens should be performed whenever there is suspicion of Whipple’s disease, to aid the diagnosis in case of negative Periodic acid-Schiff stains.•PCR testing of cerebrospinal fluid should be performed to assess for central nervous system involvement. This paper presents a case of a 51-year-old patient with chronic diarrhea, weight loss, polyarthralgia, and diffuse lymphadenopathy. Laboratory work-up showed anemia, leukocytosis and thrombocytosis, and increased C-reactive protein (CRP). Due to an inconspicuous differential leukocyte count and lymph node biopsy findings showing granulomatous lymphadenopathy, sarcoidosis was initially suspected. Colonoscopy found no abnormalities and duodenal biopsies showed negative Periodic acid-Schiff stains. However, PCR testing on these biopsies revealed Tropheryma whipplei DNA. Further PCR testing of urine and cerebrospinal fluid also revealed T. whipplei DNA. The patient was treated with ceftriaxone for 2 weeks followed by trimethoprim for a year. A rapid improvement of his symptoms was seen.