1044 - Recurrent Subtalar Cyst Presenting as Tarsal Tunnel Syndrome and Lateral Plantar Neuritis

Case Diagnosis: Tarsal Tunnel Syndrome and Lateral Plantar Neuritus Secondary to Subtalar Cyst

Case Description: A 37M who is a highly active physical therapist presented for evaluation in the outpatient PM&R clinic for an insidious one-month history of swelling and fullness in the right tarsal tunnel with resulting numbness of the lateral plantar and medial calcaneal. Right ankle x-rays were negative. Focused ultrasound examination of the right tarsal tunnel demonstrated a cyst of the right subtalar joint with resultant mass effect of the tarsal tunnel and lateral plantar nerve. Under ultrasound guidance, the cyst was aspirated 3mL improving pain to 0/10 and decreased numbness for the first week. Symptoms gradually began to return in the second week continuing to limit high-level workouts. A month later, repeat aspiration along with injection of Kenalog 40 mg was completed. Symptoms returned in a similar fashion. MRI was then obtained confirming ultrasound findings. Patient planning to undergo cyst excision and tarsal tunnel release with orthopedic surgery.

Discussions: While far less common than carpal tunnel syndrome, tarsal tunnel syndrome shares characteristics of housing tendons and nerves within a bony cup with a fibrocartilagenous roof allowing minimal space for swelling or space occupying lesions prior to detrimental effects seen in the above case. Tarsal tunnel is a rare syndrome typically going underdiagnosed. Ultrasound in this case can quickly help to determine if intrinsic causes such as tendinopathy, bony prominances, vascular insufficiency, or mass effect are contributing to the symptoms.

Conclusions: This case demonstrates the value of bedside diagnostic and therapeutic ultrasound in the outpatient PM&R clinic to provide safe and efficient care to patients. Though the patient's symptoms were not provided lasting relief from the aspiration/injection this case still illustrates the value of this diagnostic tool prior to progressing to the definitive option of surgical release.