Lyme disease is real. The bacterial infection, chiefly transmitted by deer ticks, can cause rashes, swollen joints and inflamed nerves, and usually is curable with a round of antibiotics. But doctors around the country are telling patients with common medical problems such as back pain, poor concentration and fatigue that their ailments stem from a chronic form of Lyme disease that can evade standard treatment and wreak havoc for years. To fight what they believe is a persistent infection, the doctors often order months or years of intravenous antibiotics, which can cost tens of thousands of dollars. Strong evidence isn't on their side. But in a golden age of dubious medicine, that doesn't matter.