Thanks to the Salk and Sabin vaccines, the specter of crippling polio that once made summers an apprehensive time for Americans has long since passed. Yet for many of the 300,000 living victims of that disease, there remains a frightening echo of the paralysis they suffered decades ago. This "second curse," as some have called it, is postpoliomyelitis muscular atrophy (PPMA), which manifests itself in renewed bouts of muscle weakness and unexplained fatigue. Except for its relation to childhood polio, its cause is unknown and there is no cure.

One of the foremost researchers seeking to understand PPM A is Dr. Marinos C. Dalakas, 36, a neurologist at the National Institutes of Health in Bethesda, Md. (Ironically, a patient he treated there last fall for a disease eerily like the paralysis of polio was Dr. Albert Sabin, 78, inventor of the oral polio vaccine.) The Athens-born Dalakas was trained in neurology at Rutgers University and in neuromuscular diseases at the NIH. Now in his third year of PPM A research, Dalakas reviewed for correspondent Daniel Moreau what is known so far of polio's strange reprise.

What exactly is postpoliomyelitis muscular atrophy?

It's a disease that some but not all patients who once had polio tend to get. It can affect the muscles of the arms or legs. While it affects a specific muscle, that muscle may or may not have been the one previously affected by polio. It is not a severe disease, but it is scary to people who have already lost a lot of muscle strength to polio.

What are the symptoms?

A patient might experience muscle pain in an arm, for example. Or he or she might have difficulty doing something. Patients tell me, "I can't open jars the way I used to," or "I can't climb steps." It's not excruciating pain but soreness or tenderness. Some say they feel that a particular muscle group, let's say a biceps, looks thinner. Patients might also feel fatigued.

Is PPMA a new phenomenon?

It's been known for years, so it is not new in the sense that we just discovered it. What we have done is to define and classify the symptoms, and we've done some studies to see what the causes of it might be.

When does PPMA strike?

Our study found PPMA occurring an average of 30 years after the patient developed polio.

How many PPMA cases have been reported so far?

There is no central registry so there is no way of knowing. PPMA can mimic other diseases, such as the compression of a nerve. PPMA can only be diagnosed by a neurologist, preferably one experienced in neuromuscular diseases, to eliminate other problems that resemble PPMA.

How many polio victims are likely to get PPMA?

Perhaps 15 percent of the 300,000 people alive who have had polio might develop true PPMA. I'm doing a survey now examining 2,500 patients who have had polio, and we should know more in a year or so.

What triggers PPMA?

We don't know yet. There are several theories. When we grow older, we lose a few nerve cells in the spinal cord. This loss is not noticeable because healthy cells compensate. But patients who developed polio have lost nerve cells, and the remaining healthy cells may have been overworked. This may explain the weakness that develops in muscles that had been affected by polio, but it doesn't explain the weakness in muscles that were not previously affected by it. So we're looking at other possibilities.

What other possibilities?

We are investigating whether PPMA is related to some kind of abnormality of the immune system. We're also looking at the spinal fluid for clues. An investigation like this is a long process. You may not find the answers immediately.

Is PPMA related to the so-called Lou Gehrig's disease?

Some people have linked the two, but they're totally mistaken. PPMA affects the same cells in the body, but it doesn't follow the course of Lou Gehrig's disease [amyotrophic lateral sclerosis, or ALS]. PPMA doesn't kill.

Might it merely be a reactivation of the original polio?

Although that possibility is remote, we're exploring it. While we know that poliovirus can persist in animals, we do not have any evidence yet that it persists in people with normal immune systems. It's important to emphasize that PPMA is not a recurrent polio. With PPMA you get some new muscle weakness in specific muscle groups, and the weakness increases over several years.

How does the disease progress?

Like every neurological disease the progression is hard to predict. Pain, fatigue and muscle weakness might worsen every two or three years or remain at the same level for many years. If the disease affects a muscle group that's already weak, that will be significant because a patient will lose what little strength he or she already has.

Is there a prescribed treatment?

Not yet. We are in the process of using interferon in an experimental therapy, but we've only begun.

If a polio victim suspects he now has PPMA, what should he do?

Patients complaining of new muscle weakness should seek expert medical determination of whether the cause is PPMA or something else. The main thing I can offer is reassurance to patients that this is not a life-threatening or incapacitating disease. Patients will be able to function fairly normally, so it is not a second curse.