July 20 (HealthDay News) -- A supposedly harmless condition -- superficial vein thrombosis, or varicose veins that have become swollen and painful -- may herald the presence of a more dangerous problem.

One-quarter of patients with superficial vein thrombosis (SVT) in an Austrian study actually had deep vein thrombosis (DVT), a potentially life-threatening condition.

"The diagnosis of [SVT] has long been considered to be a benign entity which could be managed in the doctor's office [but] in fact may be the tip of the iceberg," said Dr. Robert Lookstein, an associate professor of radiology and surgery at the Mount Sinai School of Medicine in New York City.

"I think it's a good idea for anybody with [superficial vein thrombosis] to undergo routine ultrasound screening of the deep veins of their legs to exclude this very, very serious diagnosis," Lookstein continued.

This advice does not apply to individuals with "regular" varicose veins, only to those who are experiencing varicose veins that are "quite engorged and firm to the touch," Lookstein said.

Many doctors may already be on the alert.

"This [finding] does not surprise me," said Dr. Robert Rosen, director of vascular intervention at Lenox Hill Hospital in New York City. "They [the study authors] are documenting something that doctors are already doing."

SVT, explained Lookstein, happens when varicose veins in the calves or thighs become filled with blood clots. "They become painful, can become hot and patients can have low-grade fevers," he said. "It's a condition that can be quite uncomfortable."

Unlike SVT, which is visible on the surface of the skin, DVT is a blood clot that forms in veins deeper in the body. Complications can include pulmonary embolism, when a piece of the clot in the leg breaks off and travels to the lung; and post-thrombotic syndrome, in which the clots in the leg never heal, sometimes leading to loss of function of the legs, Lookstein said.

"This can transform somebody who would otherwise be a working member of the community and turn them into somebody unable to work, somebody who is bedbound," he said.

The authors of the new study, from the Medical University of Graz in Austria, looked at 46 patients (32 women and 14 men) who came to the dermatology department with SVT.

One-quarter of the patients had DVT, usually without symptoms. Of these, three-quarters had DVT in the same leg as the superficial vein thrombosis, 9 percent had DVT in the other leg and 18 percent had it in both legs, the researchers said.

Anybody with SVT should undergo routine screening with duplex ultrasound, which can be performed either in a doctor's office or by a vascular specialist, Lookstein said.

The findings were published in the July issue of the Archives of Dermatology.

SOURCES: Robert Rosen, M.D., director, vascular intervention, Lenox Hill Hospital, New York City; Robert Lookstein, M.D., associate professor, radiology and surgery, Mount Sinai School of Medicine, New York City; July 2009 Archives of Dermatology