Footworks column September 2011
By Alexandra Buk, DPM
Lumps On The Bottom Of The Foot
A few months ago we reviewed the most common mass found at the top of the foot: the ganglion cyst. Today we turn our attention to the bottom of the foot, where the two most common benign tumors found are plantar fibromas and rheumatoid nodules.
Plantar fascial fibromatosis, also known as Ledderhose’s disease, is a non-malignant thickening of the foot’s deep tissue layer known as the plantar fascia. In the beginning, when the nodules or cord just begin to grow, the disease is minor. Eventually the cords thicken and walking becomes painful. The disease is named after Dr Georg Ledderhose, a German surgeon who described the condition for the first time in 1894. A similar disease is Dupuytren’s disease, which affects the hand and causes bent fingers.
As in most forms of fibromatosis, it is usually benign and its onset varies with each patient. The nodules are typically slow growing and most often found in the central and medial portions of the plantar fascia,, near the highest point of the arch. Occasionally, the nodules may lie dormant for months or years only to begin rapid and unexpected growth. The lump is usually painless and the only symptoms occur when the nodule rubs on the shoe or floor. The overlying skin is freely moveable, and usually there is no contracture or curling of the toes in the early stages.
The typical appearance of the plantar fibromatosis on MRI is a poorly defined, infiltrative mass in the tissue next to the muscles on the bottom of the foot. Only 25% of patients show symptoms on both feet.
The root causes of plantar fibromatosis are unknown, however it has been noted that it is an inherited disease, and there are certain risk factors. The disease is more commonly associated with:
- A family history of the disease
- Higher incidence in males
- Palmar fibromatosis, 10-65% of the time
- Epilepsy patients
- Patients with diabetes
There is also a suspected link between incidence and alcoholism, smoking, liver disease, thyroid problems and stressful work involving the feet.
Although the origin of the disease is unknown, there is speculation that it is an aggressive healing response to small tears in the plantar fascia, almost as if the fascia over-repairs itself following an injury. In the early stages, when the nodule is single and smaller, it is recommended to avoid direct pressure on the nodule. Soft insoles, padding or a cut-out in the orthotic can help.
MRI and diagnostic ultrasound are effective in showing the extent, size and boundaries of the lesion. The imaging characteristics can also differentiate the fibroma from other soft tissue masses such as lipomas (fatty tumors) and hemangiomas (abnormal blood vessels), thereby assisting in the clinical diagnosis.
Surgical excision of plantar fibromatosis is difficult because tendons, nerves and muscles are located very closely to each other. Since the diseased area is not encapsulated, it is difficult to clinically determine the margins of the lesion, and portions of the diseased tissue may be left in the foot after surgery. The rate of recurrence is very high following excision of plantar fibroma. Because of this non-surgical treatment such as cortisone injection, cryotherapy and topical applications of steroid or other medications should be attempted initially.
Aside from problems with small joints, the most common symptom of rheumatoid arthritis is the growth of rheumatoid nodules. About 25% of people with Rheumatoid arthritis (RA) will develop skin nodules which range in size from a pea to a mothball. They are more common in men than women, and Caucasians are more likely than other ethnicities to develop them. They are also widespread in people who test positive for rheumatoid factor, but relatively rare in those who test negative for it. (Rheumatoid factor is an antibody linked to inflammation in the body.)
The little knots of tissue are made up of inflammatory tissue. They are common in the skin but may also turn up in the lungs, heart and tendons. They usually form in areas of the body that feel pressure, such as the elbows, fingers heels and balls of the feet. Nodules are more commonly found after RA has been present for some time. They may feel firm and rubbery or soft and squishy.
Since nodules don’t generally cause any problems, they usually don’t need to be treated. However, if on the feet shoes can rub them and if on the bottom walking can become painful. In addition, the skin overlying the nodules can break down, which can lead to an open sore or infection..
Often disease-modifying anti-rheumatic drugs will help shrink down the nodules, however your podiatrist can inject it with medication to speed up the process. Surgical removal of the lesion may be required if the mass is causing nerve pain, an open sore or range of motion issues.