A young female presents with sudden onset of urinary retention. She has the urge to urinate but is unable to do so. Physical examination and medical history are unremarkable. Cystometry reveals that her bladder is hypersensitive to Bethanechol. What is the most likely diagnosis?

1) Urinary tract infection
2) Interstitial cystitis
3) Neurogenic bladder
4) Bladder outlet obstruction

The most likely diagnosis in this case is interstitial cystitis. Urinary retention, accompanied by the urge to urinate, but an inability to do so, is a characteristic symptom of interstitial cystitis. This condition is a chronic inflammation of the bladder wall and can cause hypersensitivity of the bladder, making it overly sensitive to certain medications such as Bethanechol.

Explanation:

The most likely diagnosis in this case is interstitial cystitis.

Urinary retention, accompanied by the urge to urinate, but an inability to do so, is a characteristic symptom of interstitial cystitis. This condition is a chronic inflammation of the bladder wall and can cause hypersensitivity of the bladder, making it overly sensitive to certain medications such as Bethanechol, as mentioned in the question.

While urinary tract infection, neurogenic bladder, and bladder outlet obstruction can also lead to urinary retention, the absence of significant findings in the physical examination and medical history, along with the hypersensitivity to Bethanechol, make interstitial cystitis the most likely diagnosis in this case.