When Vicki Ratner, a third-year medical student, was struck with severe bladder pain, she went to a urologist expecting another diagnosis of cystitis, a recurring urinary tract infection common in women. The pain, which wouldn't go away, "felt like I had a knife in my bladder," Ratner recalls, but the doctor could find nothing wrong.

One year and 14 doctors later, and after several hours of medical research of her own, Ratner finally received her diagnosis: interstitial cystitis (IC) -- a disease for which there is no known cause, reliable remedy or cure.

But Ratner's crusading efforts in forming the Interstitial Cystitis Association has focused attention on a disease typically relegated, as she puts it, "to wastebasket diagnoses of women's complaints."

In fact, the disease occurs in both women and men, but is more common in women.

When Ratner, now an orthopedic surgery resident at the Bronx's Montefiore Medical Center, appeared on ABC's "Good Morning America" in April, she received 10,000 letters from distraught IC victims.

Many IC victims report they cannot have sexual intercourse because of the severe pain and are confined to their homes because of the urgency to urinate 50 to 60 times a day. Some have attempted suicide, says Ratner.

Marriages have broken up and some victims have had to quit their jobs. One woman in northern New York can't travel to New York City anymore because she is unable to get through the Lincoln Tunnel without needing to urinate.

"I hate to point a finger" at the predominantly male urology speciality, Ratner says, "but women's complaints about the disease haven't been taken seriously."

Ratner considers herself lucky because her training in medical research led to a relatively quick diagnosis.

Some doctors told her it was all in her head. "Several said it was stress and would go away," she said. "I got the typical find-a-boyfriend-and-get-married response. It was humiliating. When doctors don't know what something is, they say it's psychosomatic."

"IC is real, though," says Dr. Philip M. Hanno, director of the new Women's Center for Interstitial Cystitis at the Hospital of the University of Pennsylvania in Philadelphia. The hospital is one of about a dozen IC research sites across the country.

"Many doctors are not taking IC seriously," he adds. "It's the PMS of the '80s," referring to premenstrual syndrome, which only recently has been recognized as a series of hormonal changes affecting mood and physical well-being prior to menstruation.

"People who have IC are not crazy, although they may get crazy because of it," says Hanno, who personally sees three to four new IC patients a week. About 10 to 15 percent of the cases are extremely severe, he says.

IC is difficult to diagnose. The symptoms mimic common cystitis, which usually is eased by antibiotics within 24 hours or by home remedies, such as drinking cranberry juice.

But these treatments don't relieve IC. In addition to the frequent need to urinate, there is burning during urination. Usually victims suffer severe abdominal pain, either chronic or intermittent.

Once thought to be rare, IC is now believed to be common, although no studies have been done to determine its frequency. Researchers do know the symptoms show up 10 times more often in women than men, but they do not know why.

The disease is not new -- it first was described in 1830s as an inflammation of both the bladder muscle and bladder lining and later as small ulcerations in the bladder. Yet these descriptions are insufficient compared with what doctors find today if they perform a complete diagnosis.

First doctors have to rule out regular cystitis, unusual bacterial causes (such as tuberculosis, parasites and chlamydia), kidney malfunctioning and neurological diseases (such as multiple sclerosis) which could affect the bladder, and bladder cancer, particularly in men, where bladder cancer is more common.

If a cystoscope with a fiber-optic attachment used to view the interior of the bladder does not show any disease under local anesthesia, then, with the patient unconscious, doctors must fill and stretch the bladder enough to see the tiny pinpoint hemorrhages all over the bladder wall, which are the hallmark of this disease.

Decreased bladder capacity is another sign. Because of scarring, this disease can decrease the capacity to as little as three or four ounces versus the normal 12 ounces. Finally, doctors can perform a biopsy of the bladder lining and muscle. "If they see inflammations involving both, and nothing else comes up positive, then it's IC," says Hanno.

The cause of IC is a subject of considerable speculation. One theory suggests that the body's own defense mechanisms are launching antibodies against the lining and muscles of the bladder, which causes them to deteriorate, says Hanno. Other theories include undiscovered infectious agents, stress, allergies, diet and drugs.

Dr. Larrian Gillespie, director of the Women's Clinic of Interstitial Cystitis in Los Angeles, believes antibiotics, when used in the absence of infection, may damage the protective membrane of the bladder surface.

Hanno is looking for a problem in the protective coating of the bladder, which, under normal conditions, protects against "acid burn" of urine and attachment of antibodies. Because of the predominance of the disease in women, he says, possible hormonal causes should not be overlooked.

Treatment is difficult, and nothing cures or reverses the disease. For some victims, pain medication, including low doses of codeine and anti-inflammatory medications, provide relief. But treatment may mean constant medication. Steroids are considered undesirable because they require large doses and produce side effects.

Doctors also can overfill the bladder under anesthesia for a few minutes to help break up scar tissue, soothe nerve endings and relieve pain.

The anti-inflammatory drug DMSO (dimethylsulfoxide), which has been banned by the Food and Drug Administration for other uses, was approved to treat IC in 1978. Some researchers prefer other drugs, such as applications of silver nitrate. In all treatments efforts, the results are mixed.

Surgical efforts to remove nerves in the bladder have not yielded good results. But surgeons can remove the diseased sections of the bladder and replace it with pieces of bowel. Because the reconstrusted bladder may not function normally, patients may have to be catheterized for the rest of their lives. This approach, however, is very effective, Hanno says.

Ratner, meanwhile, still suffers from IC pain. "I always know where the nearest bathroom is," she says. But hearing from 25,000 other victims since the spring of 1984 when she organized the Interstitial Cystitis Association has helped. Even physicians write to her for information.

"Now I know I'm not alone and I'm not crazy," she says. "This really has been a closet disease."