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Case report
peer-reviewed

A Morton's Neuroma Invading the Proper Digital Nerve



Abstract

We report a case of a 55-year-old female with extreme right fourth toe pain of unknown origin that was resistant to conservative care. Resection confirmed invasion of the neuroma into the fourth digit with hypertrophy and herniation of the proper digital nerve. The patient experienced an uneventful recovery with some minor neurogenic symptoms experienced at six months postoperatively that resolved with off-loading padding and heat massage. Complete pain relief was reported at her 12-month review. Isolated neuroma within a toe results in digital pain that may respond to excision.

Introduction

Neuromas of the forefoot are common conditions presenting to outpatient clinics and are generally amenable to conservative care [1-3]. Of these, Morton’s neuroma, the most common variant, was first described by Civinini in 1835 and refers to the nerve within the third intermetatarsal space [1].

There is a lack of epidemiological data regarding forefoot neuromas, and their prevalence is unknown [2]. They appear more common in females (75%-95%), and the average age of patients is 50 years [2,4,5]. High-arch feet and regularly wearing tight-fitting shoes appear to be risk factors [6].

Digital neuromas, neuromas affecting the proper digital nerve of one toe, may have a similar morphology, but to our knowledge there is no literature on their prevalence or treatment. Herein, we discuss our treatment method of such a case. To our knowledge, this is the first reported case of a proper digital neuroma within a toe.

Case Presentation

A 55-year-old female was referred reporting 12 months of extreme right fourth toe pain. She was of generally good health, taking 600 mg of lithium twice daily for bipolar disorder. She was a current smoker, averaging 10 cigarettes daily. Conservative treatments over the preceding 12 months had failed to reduce her symptoms. This included two corticosteroid injections using a betamethasone sodium acetate/lignocaine hydrochloride mix, one pair of non-prescription orthotics, physical therapy with heat massage, and several prescriptions of opioid-based analgesics.

Diagnostic ultrasound (US) showed a third webspace burial neuroma complex measuring 11 x 4.5 mm. Resection was performed via a dorsal approach (Figure 1). The specimen exhibited thickening and herniation of the proper digital branch of the fourth toe (Figure 2) which corresponded to her isolated site of pain. At six months, she experienced some mild neurogenic symptoms that were abated with off-loading padding and heat massage.

Discussion

Neuromas of the forefoot often present with intermittent lancing pain, burning and numbness of adjacent toes, or a decrease in sensation in the area of the nerve [7]. There is controversy in the literature regarding their cause, with four main theories existing [4]. First, chronic trauma, where stress from the adjacent forefoot structures causes repetitive trauma to the nerve [4]. Second, ischaemia, whereby neurofibrosis occurs from reduced blood flow to the nerve via abnormalities to the feeder artery [8,9]. Third, intermetatarsal bursitis, where there is adherence between the nerve and the bursa [10-14]. Fourth, entrapment, where the nerve becomes entrapped between the plantar aspect of the foot and the transverse intermetatarsal ligament [15].

Although their cause is controversial, the pathophysiology of forefoot neuromas remains constant. Histological studies show perineurial and epineural fibrosis, degenerative vascular changes, arrested axonal nerve endings, demyelination of the axon, fibrinoid degeneration, and an increase in sympathetic nerve fibres [8]

Neuromas invading the proper digital nerve have been previously reported in the literature but only of the fifth proper digital nerve being encountered during the correction of bunionette deformities [16]. Many anatomy texts and illustrations describe the proper digital nerve of the fifth toe as being normally enlarged and convoluted as it passes the neck and condyles of the fifth metatarsal. This cause does not appear to be the case with digital neuromas of the fourth digit.

We report a single case report of a proper digital nerve of the fourth toe that resulted in extreme pain. This appears to be the first reported case of a proper digital nerve not involving the fifth toe. 

Conclusions

This appears to be the first case in the literature of extreme isolated toe pain caused by a neuroma within the digit. Surgical resection was performed which resolved the patient's symptoms, albeit with some mild neurogenic pain arising at six months postoperatively that were abated with off-loading padding and heat massage. Surgical resection in a case of proper digital neuroma appears to provide effective pain relief and patient satisfaction.


References

  1. Civinnini F: Su d’un gangliare rigonfiamento della pianta del piede. Men Chir Arcispedale di Pistoia. dalla tip. Bracali, Pistoia, Italia; 1835.
  2. Jain S, Mannan K: The diagnosis and management of Morton’s neuroma: a literature review. Foot Ankle Spec. 2013, 6:307-317. 10.1177/1938640013493464
  3. Thomson CE, Beggs I, Martin DJ, et al.: Methylprednisolone injections for the treatment of Morton neuroma: a patient-blinded randomized trial. J Bone Joint Surg Am. 2013, 95:790-798. 10.2106/JBJS.I.01780
  4. Hassouna HS, Singh D: Morton’s metatarsalgia: pathogenesis, aetiology and current management. Acta Orthop Belg. 2005, 71:646-655.
  5. Latinovic R, Gulliford MC, Hughes RAC: Incidence of common compressive neuropathies in primary care. J Neurol Neurosurg Psychiatry. 2006, 77:263-265. 10.1136/jnnp.2005.066696
  6. Metcalfe S, Reilly I: Foot and Ankle Injection Techniques: A Practical Guide. Churchill Livingstone, London, UK; 2010.
  7. Weinfeld SB, Myerson MS: Interdigital neuritis: diagnosis and treatment. J Am Acad Orthop Surg. 1996, 4:328-355. 10.5435/00124635-199611000-00005
  8. Betts LO: Morton’s metatarsalgia neuritis of the fourth digital nerve. Med J Aust. 1940, 1:514-515.
  9. Nissen KI: Plantar digital neuritis; Morton’s metatarsalgia. J Bone Joint Surg Br. 1948, 30:84-94.
  10. Hingertz N, Unander-Scharin L: Morton’s disease: a clinical and patho-anatomical study. Acta Orthop Scand. 1950, 19:327-348.
  11. Meachim G, Abberton MJ: Histological findings in Morton’s metatarsalgia. J Pathol. 1971, 103:209-217.
  12. Mulder JD: The causative mechanism in Morton’s metatarsalgia. J Bone Joint Surg Br. 1951, 33:94-95.
  13. Bossley CJ, Cairney PC: The intermetatarsophalangeal bursa: its significance in Morton’s metatarsalgia. J Bone Joint Surg Am. 1980, 62:184-187.
  14. Awerbuch MS, Shephard E, Vernon-Roberts B: Morton’s metatarsalgia due to intermetatarsophalangeal bursitis as an early manifestation of rheumatoid arthritis. Clin Orthop Relat Res. 1982, 167:214-221.
  15. Gauthier G: Thomas Morton’s disease: a nerve entrapment syndrome. A new surgical technique. Clin Orthop Relat Res. 1979, 142:90-92.
  16. Feller SR, Evans RD: Proper digital neuroma of the fifth toe. J Am Podiatr Med Assoc. 1996, 86:187-188.
Case report
peer-reviewed

A Morton's Neuroma Invading the Proper Digital Nerve


Author Information

Steven R. Edwards Corresponding Author

Surgery, Australasian College of Podiatric Surgeons, Melbourne, AUS

Podiatry, La Trobe University, Bundoora, AUS

Dean Samaras

Podiatric Surgery, Australasian College of Podiatric Surgeons, Melbourne, AUS


Ethics Statement and Conflict of Interest Disclosures

Human subjects: Consent was obtained by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Acknowledgements

We wish to thank Dr. George Koulouris for reporting the radiology results and Dr Glenn Hocking for reporting the histopathology results.


Case report
peer-reviewed

A Morton's Neuroma Invading the Proper Digital Nerve


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