A 44-year-old woman presents to the clinic with a 6-month history of pain in her left forefoot. She describes the sensation as "walking on a marble" or having a "stone in her shoe." The pain radiates to her third and fourth toes and is significantly worse when she wears her favorite pointed-toe high heels. It is relieved when she takes off her shoes and massages her foot. Past medical history is negative. On physical examination, there is no visible swelling or redness. When the clinician compresses the metatarsal heads together with one hand and applies pressure to the third intermetatarsal space with the other, a palpable click is felt, which reproduces the patient's pain.
Which of the following is the most likely diagnosis?
The correct answer is:
C) Morton neuroma
This patient is presenting with a classic case of Morton neuroma. Despite the name, it is not a true neuroma but rather a compressive neuropathy and perineural fibrosis of the common plantar digital nerve. It most commonly occurs in the third intermetatarsal space between the 3rd and 4th metatarsal heads. Patients often describe a burning sensation or the feeling of a foreign body in their shoe. Activities or footwear that increase pressure on the forefoot, like high heels or tight-fitting shoes, exacerbate the condition. The Mulder sign is highly suggestive. This is the palpable click or pop elicited by squeezing the metatarsal heads together while applying pressure to the interdigital space.
Answer choice A: Freiberg infraction, is incorrect. This is an avascular necrosis of the second metatarsal head, typically seen in adolescent girls. While it causes forefoot pain, it usually presents with swelling and tenderness over the dorsal aspect of the joint, and X-rays would show flattening of the metatarsal head.
Answer choice B: Metatarsal stress fracture, is incorrect. This usually presents with localized point tenderness over the shaft of the metatarsal and dorsal swelling. Pain is typically related to increased weight-bearing activity rather than specific footwear types.
Answer choice D: Plantar fasciitis, is incorrect. Plantar fasciitis involves the heel, with maximal tenderness at the calcaneal insertion.
Answer choice E: Rheumatoid nodule, is incorrect. While rheumatoid arthritis can cause nodules on pressure points, like the Achilles or elbows, and can lead to metataro-phalangeal (MTP) joint inflammation, it would not typically present as an isolated interdigital nerve entrapment with a Mulder click. Also, this patient does not have a history of rheumatoid arthritis.
Key Learning Point
Morton neuroma is a degenerative/fibrotic condition of the interdigital nerve, most common in the 3rd interspace. Diagnosis is clinical, based on the "walking on a marble" sensation and a positive Mulder sign. Management begins with conservative measures, including switching to wide-toe-box shoes, using metatarsal pads, or corticosteroid injections.
