Which of the following is NOT a condition on the differential diagnosis of acute monoarthritis?

Acute monoarthritis refers to inflammation in a single joint that can arise from a variety of underlying conditions. Gout and pseudogout are both crystal-induced arthropathies, commonly resulting in acute monoarthritis. Gout is often associated with the deposition of urate crystals, while pseudogout involves calcium pyrophosphate crystals. Both conditions typically present with sudden onset of pain, swelling, and redness in the affected joint.

Rheumatoid arthritis, while usually presenting as a polyarthritis condition, can occasionally manifest initially as monoarthritis in some cases, particularly in its early stages or during flares. Thus, it remains a relevant part of a differential diagnosis, even if it is less common.

Cholecystitis, on the other hand, is an inflammation of the gallbladder usually due to gallstones and presents with abdominal symptoms rather than joint symptoms. It does not correlate with joint involvement and therefore is not considered in the differential diagnosis of acute monoarthritis. This makes it the correct answer, distinguishing it clearly from the typical causes of acute monoarthritis which primarily involve inflammatory or crystal-related conditions affecting the joint.