Sudden Intermittent Pain in 4 Year Old's Urethra

Rather odd, for sure. I wouldn't rule out UTI, because symptoms can vary quite a bit. I'd push liquids, including cranberry juice – further reactions today may help you determine whether emergency care is a good idea. You could be in for a very long night. Hope this settles down.

Muscular spasm is another possibility. My hunny has suffered from anal spasms for most of his life, and they can come out of nowhere, last for a day or two, and disappear. They can be very painful.

I'm betting its a UTI. That's exactly how I feel when I get them. The pain that I experience is not just when going to the bathroom...it is all the time and it is excruciating. I swear I'd rather be in labor than have a UTI.
its just peeing in a cup at the doctors....I'd get it checked.

Take her to the ER or at least an outpatient clinic in the next 24 hours.

Any child acting out in pain should definitely see the dr. Take her to the pediatrician's office. For future reference, always call the ped and ask; even after hours they will call you back and tell you if you should do something now or wait and come in tomorrow.

Any chance AT ALL that she might be constipated? Our daughter went thru a period of time around that age when she would suddenly writhe in horrendous pain, couldn't really tell eXACTLY where it hurt but she would point down there, and we didn't think she could possibly have been constipated, because she went to the bathroom all the time and pooped regularly. Well, after some time and multiple trips to the doctor (all testing for UTI's, yeast infections, etc with NO success) we requested referral to a children's specialist. They thought they knew what it was, did an x-ray to confirm... yep. Impacted poop. It would occasionally press against her bladder and cause it to spasm. A long weekend with multiple doses of MOM (Milk of Magnesia) cleaned her out completely, we retrained her - and her bowels - to eliminate fully, not just enough to stop the urge, and we have had no problems since.

Just an idea...

well, I'd give her some cranberry juice for now, and definitely call the pediatrician in the morning. Could be a uti, maybe swab the area with some neosporine before bed. She may even have some gas, and got a little bit of cramping. Get her the juice and swab her and tell her this will "fix it"... and maybe it will, the power of suggestion works wonders sometimes.

You say she drastically overreacts, but she doesn't usually scream like that...so it is different this time. With screaming like that, at least take her to the doctor.