Differential Diagnosis for Focal Colonic Disease Causing FUO
Given the clinical presentation of a 48-year-old man with intermittent fever of unknown origin (FUO) for 4 months, extensive negative serological and microbiology evaluations, hepatosplenomegaly on CT imaging, and focal increased metabolic activity in the sigmoid colon on whole body PET-CT without corresponding abnormalities on CT, the following differential diagnoses are considered:
Single Most Likely Diagnosis
- Diverticulitis: This condition is a common cause of focal colonic disease and can lead to intermittent fever. The presence of focal increased metabolic activity in the sigmoid colon on PET-CT, a common site for diverticula, supports this diagnosis. Chronic or recurrent diverticulitis could explain the prolonged course of FUO.
Other Likely Diagnoses
- Colonic Neoplasm: Although the CT imaging appeared normal, the increased metabolic activity on PET-CT could indicate a malignant process, such as adenocarcinoma. Early or small lesions might not be visible on CT.
- Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause FUO and have focal areas of involvement. The absence of typical symptoms (e.g., diarrhea, abdominal pain) does not rule out IBD, as extraintestinal manifestations can sometimes dominate the clinical picture.
- Colonic Lymphoma: This is another consideration for focal colonic disease with increased metabolic activity on PET-CT. Lymphoma can cause systemic symptoms, including fever.
Do Not Miss Diagnoses
- Infectious Colitis: Certain infectious agents (e.g., CMV, tuberculosis) can cause colitis and FUO. These conditions require specific diagnostic tests and treatments, making them crucial not to miss.
- Ischemic Colitis: Although less likely to cause FUO, ischemic colitis can have a varied presentation and might show increased metabolic activity on PET-CT due to inflammation.
Rare Diagnoses
- Eosinophilic Colitis: A rare condition characterized by eosinophilic infiltration of the colon, which can cause systemic symptoms, including fever.
- Amyloidosis: Systemic amyloidosis can involve the gastrointestinal tract and cause a variety of symptoms, including FUO. The hepatosplenomegaly could be related to amyloid deposition in these organs.
- Colonic Vasculitis: Vasculitis affecting the colon, such as in systemic lupus erythematosus or polyarteritis nodosa, is rare but could explain the clinical findings.