Diagnosis

The diagnosis is mainly clinical and further investigations are done as required to rule out other possible causes (1):

• clinical examination is the mainstay of diagnosis with pain at the intermetatarsal space rather than on the plantar or dorsal aspects of the MTPJs
  • neuroma generally located at the level of and just distal to the metatarsal heads
  • there may be some dorsal MTPJ tenderness due to retraction of the toes as they try to reduce pressure from beneath the ball of the foot
  • compression of the forefoot with pressure at the intermetatarsal space often elicits a click as the nerve is pushed between the metatarsals (termed a Mulder's click) - compression of the forefoot in this manner may or may not be symptomatic
  • there may be a reduction in sensation to the associated web space
• x-ray - useful in ruling out musculoskeletal pathology (neuromas are not visible) (1)
• ultrasound (US) and magnetic resonance imaging (MRI) scans are both helpful in the diagnosis and can help to differentiate diagnosis, although sensitivity and specificity can be examiner-dependent
  • US
    • considered by many as the diagnostic test of choice
    • reported to be between 94% and 100%
    • appears as an ovoid, hypoechoic mass just proximal to the metatarsal heads
    • finding a sonographic mass supports the clinical diagnosis but the absence of a mass does not exclude Morton’s neuroma (3)
  • MRI.
    • routine use is not recommended
    • used for atypical presentation and to rule out multiple neuromas (1)

One prospective study which evaluated the accuracy of pre-operative clinical assessment, US and MRI concluded that

• clinical assessment was the most sensitive and specific modality
• US and MRI had similar accuracy but was dependent on size
• accuracy of US was less for small lesions (4)

Reference:

• (1) Clinical Practice Guideline Forefoot Disorders Panel et al. Diagnosis and treatment of forefoot disorders. Section 3. Morton's intermetatarsal neuroma. J Foot Ankle Surg. 2009;48(2):251-6
• (2) ARC. Common foot disorders. Hands On 2006;10:1-6.
• (3) Hassouna H, Singh D. Morton's metatarsalgia: pathogenesis, aetiology and current management. Acta Orthop Belg. 2005;71(6):646-55
• (4) Sharp RJ et al. The role of MRI and ultrasound imaging in Morton's neuroma and the effect of size of lesion on symptoms. J Bone Joint Surg Br. 2003;85(7):999-1005