There are numerous other causes for pain on the bottom of the heel besides plantar fasciitis, tarsal tunnel syndrome, and bursitis. These causes are far less common than the others combined, but do develop from time to time.
Lower back spinal disease:
The lower back is home to the end of the spine, and subsequently nerves that supply the legs with sensation and muscle control. In a process similar to the above tarsal tunnel syndrome, spinal nerve root branch damage through arthritis or a slipped disk can create pain that is felt further down in the leg. Back pain usually accompanies this, but not always. The typical symptoms including an electrical shooting, tingling, or burning down the leg, but the symptoms can also be much more limited in some cases. If specific parts of the nerve root branch are affected, the heel or arch may be the only part of the foot that feels painful. The heel itself may be painful to the touch, but in this case it is most often due to oversensitization of the pressure receptors in the foot as a result of the lower back nerve damage. Heel pain in this situation does not respond well to treatment of the foot itself, and the lower back must be addressed. Unfortunately, this connection is difficult for people with no medical training to accept, as it is hard to conceptualize that the lower back can cause foot pain, and treatment recommendations are often dismissed or ignored.
Stress fracture of the heel bone (calcaneus):
Stress fractures of the stout heel bone are uncommon, but can develop and are misinterpreted as plantar fasciitis. Stress fractures can take several months to appear on x-rays, and when they do appear in the heel bone they can be difficult to see. For this reason stress fractures are often missed initially. Imaging studies like MRI or a bone scan can demonstrate stress fractures early on, but unless one is suspected these expensive tests are rarely performed in the initial stages of heel pain treatment. The foot needs to be immobilized for treatment and heel pain relief, and many traditional aspects of plantar fascia treatment, like anti-inflammatory medications, will actually stress fracture healing.
Inflammation from rheumatoid arthritis and other inflammatory diseases:
There are a whole group of conditions that cause inflammation throughout the body to bone and joint tissue. These conditions are called systemic arthropathies, and there are numerous diseases in this category. Fibromyalgia is also part of this group. Some inflammatory bowel diseases can also cause bone and joint pain, especially in the heels. The tissue covering the bottom of the heel bone will become inflamed and painful, and fluffy bone spurring can occur. Differentiating these conditions from plantar fasciitis can be difficult, as the heel is painful in a similar location in each condition. The contribution of these conditions should be considered when heel pain is not responding to traditional treatment.
Bone tumors do develop in the foot, both benign and malignant, and some cancers elsewhere in the body can metastasize to the foot. Malignant bone cancer in the foot is RARE, but it can happen and in its early states can cause heel pain if the heel bone is involved. More commonly, but still rare overall, benign bone tumors can develop that cause similar heel pain. Most of the time these lesions are seen on regular x-ray, but in their earliest stages no bone changes are immediately visible. Despite their rarity, if heel pain does not respond at all to treatment, repeat x-rays are a good idea to rule out these rare tumors, and any suspicious findings should be followed up with a CT or an MRI. Benign bone tumors are usually easily addressed by simple removal and bone packing to fill the resulting gap, but malignant life-threatening tumors may need more aggressive care, including leg amputation to save one’s life.
A simple cause of heel pain on the bottom of the heel can include issues found directly on the skin, such as calluses and warts. Callus do form on the heel skin as they do elsewhere, and often when on the bottom of the heel can have a hard central core that can be painful to walk on. Additionally, viral infections can cause hard lesions to form on the heel (as well as elsewhere on the bottom of the foot). Known as warts, these sometimes painful skin lesions may last for many years if untreated, and can make bearing weight painful.
A final common cause of heel pain that does not involve the plantar fascia can be the retention of a foreign body in the skin or deep heel tissue from a previous puncture wound. Puncture wounds of small sharp objects can sometimes be missed or dismissed as a more minor injury. The material that is left behind in the skin will cause an inflammatory reaction, and even be walled off by the body inside a capsule of sorts. The resulting inflammation and/or mass in the heel will cause heel pain, and can be mistaken for plantar fasciitis if it is in a specific location.