It sounds as though it could be Pith Necrosis, which is a systemic bacterial disease.

But here are a few questions.

What was this tomato growing in, local soil or artificial mix?

How often were you fertilizing it and with what and how much? I ask only b'c it's one of the contributing factors to Pith Necrosis.

How many other tomatoes were you growing under the same conditions and did any of them come down with the same symptoms?

Where do you live, in a geographical sense, since many systemic diseases are quite localized.

Why don't you Google Pith Necrosis and see if the symptoms match what you saw.

Hope that helps.

Carolyn

i had 7 tomatoes in containers planted with bacto potting soil. I was using miracle grow nursery fert. Not sure the strenght as it is out in the greenhouse right now. Probably was giving them it too often as i didnt keep track.

I noticed today that they are all starting to develop the same synptoms. I'm in se okla.

I also had malithion dust on them. I didnt notice any dark area inside the stem, but hollow. Anyway i think it could of been either the malithion damage or as you said pith necrosis. both have some of the same symptoms and outcome.