Because Blackwell, 67, is a diabetic, the blister became infected.
He could not feel the pain from his wound because the retired Jacksonville firefighter also suffers from peripheral neuropathy, in which the nerves that transmit information from the brain to every other part of the body are damaged.
Now pain management specialists have discovered several new ways to help the millions of patients with the condition.
Nearly 4 percent of people in the United States have been diagnosed with diabetes, with half suffering some degree of peripheral neuropathy. Symptoms include numbness or loss of feeling in the hands or feet.
Patients also experience burning, aching pain and unusual sensitivity. The bundles of nerves are extremely sensitive, and pain is easily triggered.
Other causes of peripheral neuropathy include alcoholism, infection and tumors. The chronic pain also can cause anxiety and depression.
The condition is difficult to treat because everyone responds differently, and symptoms vary among patients, said Desmond Bell, a Jacksonville podiatrist and certified wound specialist.
It is very common for patients with diabetic peripheral neuropathy to walk around with a nail or piece of glass in their foot and not realize it, he said.
Treatments for diabetic peripheral neuropathy and its complications range from topical to pharmacological, with a total annual cost of about $11 billion, according to a study published by the American Diabetes Association.
Two new drugs approved by the U.S. Food and Drug Administration for the condition include duloxetine, which works on nerve pathways telling the spinal cord not to send pain, and pregabalin, an anti-convulsion drug, decreases the transmission of pain.
Both were discussed during an American Medical Association presentation in Washington last month.
Some anti-depressant medications and anti-seizure medications also have been used successfully in managing the condition, Bell said.
Two new medications unveiled in September showing promise include Cymbalta and Lyrica to help reduce pain, he said.
A device called Anodyne is a non-invasive way some physicians treat the condition where patients apply pads from the device to their extremities, and a special unit transmits infrared energy to the affected area.
This increases nitric oxide, which affects nerve transmission and circulation, he said.
Physicians say a patient's first tool in managing diabetic peripheral neuropathy pain is education about the condition.
Keeping blood sugar levels stable and protecting the feet are also key, as is participating in physical activity, and psychological treatment for depression can also help with pain.
"Damaged nerves are like wires without insulation -- they can start a sparking on their own, creating a spontaneous generation of sensations to the brain," said Sean Mackey, associate director of the Stanford University Pain Management Center in Stanford, Calif.
"Imagine combining those aches and pains with the sparking sensations from nerve damage. It's a public health problem today that will only get worse with increasing diabetes rates, including in children."