The most common symptom of an interdigital neuroma is pain in the forefoot that radiates to the digits. Pain may also radiate proximally or to the dorsal aspect of the foot. Patients typically describe a burning pain that is accompanied by the feeling of electric shocks or a painful numbness. Symptoms may increase when walking barefoot or while wearing tight or high-heeled shoes. Interdigital neuromas often affect women in their fifth decade of life. Although no specific time frame has been identified, neuroma symptoms appear to be a chronic condition.

The third common digital nerve is the most frequently affected nerve. Second-interspace pain is usually capsular in origin, and neuromas are much more likely to be misdiagnosed in this interspace. The occurrence rate of second-interspace neuromas versus third-interspace neuromas varies in the literature. Coughlin and Pinsonneault (8) excised a total of 74 neuromas from 66 patients and found that 22% of the neuromas occurred within the second interspace and 78% occurred in the third interspace. This is similar to Dockery’s (9) findings in which he reported an 80% occurrence rate in the third interspace. Womack et al (10) retrospectively reviewed 120 patients. Patients with second-interspace neuromas had significantly lower visual analog scale scores than those with third-interspace neuromas. Conversely, Keh et al (11) looked at 70 neuromas, and 67% were located within the second interspace. In 1983, Mann and Reynolds (12) found equal success rates with second-and third-interspace neuromas. A different diagnosis should be sought if symptoms occur in the first and fourth interspace.

Clinical examination reveals marked palpatory pain between the distal aspect of the metatarsal heads and the bases of the adjacent digits in the involved interspace. Pain between the plantar aspect of the metatarsal heads or with range of motion of the metatarsal phalangeal joints is not consistent with a neuroma. A “clicking” can often be palpated when pushing upward between the phalangeal bases and applying lateral compression to the metatarsal heads. This is a classic Mulder sign. Unfortunately, this test is not sine qua non for neuromas as it can often be elicited in normal interspaces as well. If examination reveals a Tinel or “electric” sensation with compression, the most likely diagnosis is a neuroma. A true Morton neuroma will also exhibit sensory changes in one or both sides of the affected interspace. Diagnostic injections are of little value in the accurate diagnosing of interdigital neuromas. Younger and Claridge (13) observed the surgical outcome of a series of patients that all had a surgical excision of an interdigital neuroma following a positive diagnostic block. The authors found that diagnostic injections do not correlate to a favorable surgical outcome.

In addition to diagnostic injections, MRI and ultrasound imaging may be utilized by the physician to achieve an accurate preoperative assessment. Sharp et al (14) found that the history and physical exam was the most sensitive and specific modality compared to MRI and ultrasound in diagnosing Morton neuroma in 29 cases. Other studies have shown ultrasound to be fairly accurate. Despite this, clinical assessment is still the most helpful in diagnosis.