Is Morton’s neuroma a nerve entrapment syndrome?
Morton’s neuroma is really a “nerve entrapment” syndrome. So what does that mean?
Morton’s neuroma was first described in 1958 as a neuroma (or nerve tumor) but is not a neuroma and it is not tumor. Morton’s neuroma is a nerve entrapment syndrome. Despite extremely high prevalence in the general population, Morton’s neuroma is very frequently misunderstood by patients as well as physicians.
What should you know about Morton’s neuroma and entrapment neuropathy?
According to latest estimates, the prevalence of Morton Neuroma is as high as 33% in the general population(1). Morton’s neuroma can be a difficult diagnosis because a fair percentage of Morton neuroma cases can mimic common musculoskeletal conditions like tarsal tunnel syndrome, hammertoe, arthritis, ganglion cyst, bursitis, metatarsophalangeal subluxation, foreign body granuloma, or nerve tumors(2).
Women are more likely to develop Morton neuroma as compared to males. The histopathology (or tissue findings) of Morton’s neuroma are fairly similar to other entrapment neuropathies such as Carpal tunnel syndrome with areas of perineural fibrosis.
The pathophysiology of Morton neuroma revolves around the compression of common plantar digital nerve (also referred to as intermetatarsal nerve) due to persistent exposure to pressure as a result of overcrowding or overriding phenomena of metatarsal heads. The common risk factors that may aggravate the risk of overcrowding are:
- Improper or ill-fitting footgear (i.e. narrow-mouth shoes, high heels, constricted toe-box shoes etc.)
- Congenital or acquired deformities of foot
- Female gender
- Certain occupational or recreational activities that involves excessive wear and tear along the transverse intermetatarsal ligament
So, why Morton neuroma is not a nerve tumor?
A typical neuroma or nerve tumor is a benign or malignant growth that usually arises from the nerve tissues to cause pain and sensory/ motor deficits. The American College of Foot and Ankle Surgeons defines Morton neuroma as compression neuropathy of the intermetatarsal nerve or common digital nerve.
Morton’s neuroma is not a tumor or abnormal growth because:
- A neuroma or abnormal growth involving a nerve is usually a result of nerve injury or malignant transformation whereas Morton’s neuroma is a result of nerve compression and degeneration.
- A nerve tumor is a growth whereas Morton’s neuroma is merely swelling or thickening of interdigital nerve at the site of bifurcation.
- On histological examination, nerve tumors are specific for abnormal nerve (neural) cells while Morton’s neuromas are specific perineural and endoneural fibrosis. In fact, based on the histological features and pathophysiological characteristics, Morton neuroma can be labeled as perineural fibroma – a term that denotes the formation of fibrotic tissue around the involved nerve as part of the inflammatory process.
- The clinical diagnosis of Morton’s neuroma involves detailed history and physical examination. In most cases, no sophisticated imaging like MRI, nerve conduction studies etc. is needed to establish the diagnosis of Morton neuroma(3) unlike a typical nerve tumor.
- Morton’s neuroma is ideally managed conservatively, or with Ultrasound guided ablation procedures while surgical resections are usually the preferred mode of therapy for neuromas.
- Although surgery is often a last resort, Morton’s neuroma is the only form of entrapment neuropathy where surgeons resect the nerve to alleviate the symptoms of the nerve dysfunction
Morton’s neuroma can be best explained as a swollen, inflamed nerve that may compromise your productivity and mobility if not managed adequately. It is highly recommended to see a healthcare professional in order to address that gnawing, burning pain in your foot. For information on the diagnosis of Mortons neuroma click here. For information on the treatment of Mortons neuroma click here.
- Valero, J., Gallart, J., González, D., Deus, J., & Lahoz, M. (2014). Multiple Interdigital Neuromas: A Retrospective Study of 279 Feet with 462 Neuromas. The Journal of Foot and Ankle Surgery.
- Richardson, D. R., & Dean, E. M. (2014). The Recurrent Morton Neuroma: What Now?. Foot and ankle clinics, 19(3), 437-449.
- Xu, Z., Duan, X., Yu, X., Wang, H., Dong, X., & Xiang, Z. (2014). The accuracy of ultrasonography and magnetic resonance imaging for the diagnosis of Morton’s neuroma: a systematic review. Clinical radiology.