Morton's neuroma

Morton's neuroma
Classification and external resources
The plantar nerves.
ICD-10	G57.6
ICD-9	355.6
DiseasesDB	8356
eMedicine	orthoped/623 pmr/81 radio/882

Morton's neuroma (also known as Morton's metatarsalgia, Morton's neuralgia, plantar neuroma and intermetatarsal neuroma) is a benign neuroma of an intermetatarsal plantar nerve, most commonly of the third and fourth intermetatarsal spaces.

This problem is characterised by pain and/or numbness, sometimes relieved by removing footwear.

Despite the name, the condition was first correctly described by a chiropodist named Durlacher,^[1] and although it is labeled a "neuroma", many sources do not consider it a true tumor, but rather a perineural fibroma (fibrous tissue formation around nerve tissue).

Symptoms and signs

Symptoms include: pain on weight bearing, frequently after only a short time. The nature of the pain varies widely among individuals. Some people experience shooting pain affecting the contiguous halves of two toes. Others describe a feeling like having a pebble in your shoe. Burning, numbness, and paresthesia may also be experienced. ^[2]

Morton's neuroma lesions have been found using MRI in patients without symptoms.^[3]

Diagnosis/differential diagnosis

Negative signs include no obvious deformities, erythema, signs of inflammation, or limitation of movement. Direct pressure between the metatarsal heads will replicate the symptoms, as will compression of the forefoot between the finger and thumb so as to compress the transverse arch of the foot. This is referred to as Mulder’s Sign.^{[citation needed]}

There are other causes of pain in the forefoot. Too often all forefoot pain is categorized as neuroma. Other conditions to consider are capsulitis, which is an inflammation of ligaments that surrounds two bones, at the level of the joint. In this case, it would be the ligaments that attach the phalanx (bone of the toe) to the metatarsal bone. Inflammation from this condition will put pressure on an otherwise healthy nerve and give neuroma-type symptoms. Additionally, an intermetatarsal bursitis between the third and fourth metatarsal bones will also give neuroma-type symptoms because it too puts pressure on the nerve. Freiberg's disease, which is an osteochondritis of the metatarsal head, causes pain on weight bearing or compression.^{[citation needed]}

Histopathology

Microscopically, the affected nerve is markedly distorted, with extensive concentric perineural fibrosis. The arterioles are thickened and occlusion by thrombi are occasionally present.^[4][5]

Imaging

Though a neuroma is a soft tissue abnormality and won’t be visualized on standard radiographs, the first step in the assessment of forefoot pain is an X-ray in order to evaluate for the presence of arthritis and exclude stress fractures/reactions and focal bone lesions, which may mimic the symptoms of a neuroma. Ultrasound (sonography) accurately demonstrates thickening of the interdigital nerve within the web space of greater than 3mm, diagnostic of a Morton’s neuroma. This typically occurs at the level of the intermetatarsal ligament. Frequently, intermetatarsal bursitis coexists with the diagnosis. Other conditions that may also be visualized with ultrasound and can be clinically confused with a neuroma include synovitis/capsulitis from the adjacent metatarsophalangeal joint, stress fractures/reaction, and plantar plate disruption.^[6][7] MRI can similarly demonstrate the above conditions; however, in the setting where more than one abnormality coexists, ultrasound has the added advantage of determining which may be the source of the patient’s pain by applying direct pressure with the probe. Further to this, ultrasound can be used to guide treatment such as cortisone injections into the webspace, as well as alcohol ablation of the nerve.

Treatment

Orthotics and corticosteroid injections are widely used conservative treatments for Morton’s neuroma. In addition to traditional orthotic arch supports, a small foam or fabric pad may be positioned under the space between the two affected metatarsals, immediately behind the bone ends. This pad helps to splay the metatarsal bones and create more space for the nerve so as to relieve pressure and irritation. It may however also elicit mild uncomfortable sensations of its own, such as the feeling of having an awkward object under one's foot. Corticosteroid injections can relieve inflammation in some patients and help to end the symptoms. For some patients, however, the inflammation and pain recur after some weeks or months, and corticosteroids can only be used a limited number of times because they cause progressive degeneraton of ligamentous and tendinous tissues.

Sclerosing alcohol injections are an increasingly available treatment alternative if the above management approaches fail. Dilute alcohol (4%) is injected directly into the area of the neuroma, causing toxicity to the fibrous nerve tissue. Frequently, treatment must be performed 2-7 times, with 1-2 weeks between interventions. An 82-90% success rate has been achieved in clinical studies, equal to or exceeding the success rate for surgical neurectomy with fewer risks and less significant recovery.^[8]

If such interventions fail, patients are commonly offered surgery known as neurectomy, which involves removing the affected piece of nerve tissue. Postoperative scar tissue formation (known as stump neuroma) can occur in approximately 20% of cases, causing a return of neuroma symptoms.^[9] Neurectomy can be performed using one of two general methods. Making the incision from the dorsal side (the top of the foot) is the original, traditional method but requires cutting the transverse ligament that connects the 3rd and 4th metatarsals in order to access the nerve beneath it. This results in exaggerated postoperative splaying of the 3rd and 4th digits (toes) due to the loss of the supporting ligamentous structure. This has aesthetic concerns for some patients and possible though unquantified long-term implications for foot structure and health. Alternatively, making the incision from the ventral side (the sole of the foot) allows more direct access to the affected nerve without cutting other structures. However, this approach requires a greater post-operative recovery time where the patient must avoid weight bearing on the affected foot because the ventral aspect of the foot is more highly ennervated and impacted by pressure when standing.

Cryogenic neuroablation is a lesser known alternative to neurectomy surgery. Cryogenic neuroablation (also known as cryo injection therapy or cryosurgery) is a term that is used to describe the destruction of axons to prevent them from carrying painful impulses. This is accomplished by applying extremely low temperatures of between −50C to −70C to the nerve-neuroma.^{[citation needed]} This results in degeneration of the intracellular elements, axons, and myelin sheath (which houses the neuroma) with wallerian degeneration. The epineurium and perineurium remain intact, thus preventing the formation of stump neuroma. The preservation of these structures differentiates cryogenic neuroablation from surgical excision and neurolytic agents such as alcohol. An initial study showed that cryo neuroablation is initially equal in effectivenesss to surgery but does not have the risk of stump neuroma formation.^[10] Longer term, cryogenic neuroablation has a higher recurrence rate of the original neuroma symptoms than surgery.

Morton's neuroma in popular culture

Dorothy Zbornak, a character in the NBC television show "The Golden Girls," was diagnosed with a Morton's Neuroma in the episode titled "The Operation."

References

1. ^ Morton's Neuroma: Interdigital Perineural Fibrosis - Wheeless' Textbook of Orthopaedics
2. ^ SimonMoyes.co.uk. What is Morton's Neuroma?. http://simonmoyes.co.uk/2011/03/09/what-is-morton%e2%80%99s-neuroma/. 
3. ^ Bencardino J, Rosenberg ZS, Beltran J, Liu X, Marty-Delfaut E (September 2000). "Morton's neuroma: is it always symptomatic?". AJR Am J Roentgenol 175 (3): 649–53. PMID 10954445. http://www.ajronline.org/cgi/pmidlookup?view=long&pmid=10954445. 
4. ^ Reed RJ, Bliss BO. Morton's neuroma. Regressive and productive inter metatarsal elastofibrositis. Arch Pathol 1973, 95: 123-129.
5. ^ Scotti TM. The lesion of Morton's metatarsalgia (Morton's toe). Arch Pathol 1957, 63: 91-102.
6. ^ Gregg JM, Schneider T, Marks P (2008). "MR imaging and ultrasound of metatarsalgia--the lesser metatarsals". Radiol Clin North Am 46 (6): 1061–78. PMID 19038613. 
7. ^ Gregg JM, Marks P (2007). "Metatarsalgia: an ultrasound perspective". Australas Radiol 51 (6): 493–9. PMID 17958682. 
8. ^ Dockery, 1999. http://www.drvolpe.it/pat_sindrome_morton.asp
9. ^ NHS.CO.UK. treating Morton’s neuroma. http://www.nhs.uk/Conditions/mortonsneuroma/Pages/treatmentpage.aspx. 
10. ^ A Caporusso EF, Fallat LM, Savoy-Moore R. (Sept-Oct 2002). "Cryogenic Neuroablation for the treatment of lower extremity neuromas". J Foot Ankle Surg. 41 (5): 286–290. doi:10.1016/S1067-2516(02)80046-1. PMID 12400711. http://www.ncbi.nlm.nih.gov/sites/entrez?db=PubMed&cmd=Search&term=cryogenic+neuroablation+for+the+treatment+of+lower+extremity+neuromas&doptcmdl=Books&log%24=bookpubmed&bname=helppubmed. 

External links

• Overview at Mayo Clinic
• Podiatry Channel
• -664076278 at GPnotebook
• American Orthopaedic Foot and Ankle Society
• American Academy of Podiatric Sports Medicine
• Morton's Neuroma . Net
• Morton's Neuroma.co.uk
• Morton's Neuroma Blog
• Image gallery of MRI & Ultrasound evaluation of forefoot pain
• What is Morton's Neuroma - www.SimonMoyes.co.uk