(Kiosk 2) Lacertus Syndrome Diagnosed by Physical Exam and Ultrasound: A Case Report

Case Diagnosis: Lacertus syndrome in a 27-year-old right hand dominant female

Case Description or Program Description: Patient presented to plastic surgery for evaluation of several year history of right-hand weakness with numbness and paresthesias primarily in digits 1-3. Examination at that time was concerning for possible carpal and cubital tunnel syndrome. Previous limited electrodiagnostic testing performed by another department only revealed borderline carpal tunnel syndrome. Patient was referred for diagnostic ultrasound evaluation. Physical exam of the right upper extremity was notable for a positive Tinel’s both at the lacertus fibrosus (LF) and wrist; as well as flexor pollicis longus (FPL) weakness. Diagnostic ultrasound examination of median nerve showed increased cross-sectional area (CSA) of median nerve at the lacertus fibrosus of 13mm2 (normal ≤9 mm2) with perineural swelling and focal narrowing across the LF on longitudinal axis. Sonopalpation at the LF caused a positive Tinel’s. CSA at the carpal inlet was borderline at 10 mm2. Wrist: forearm ratio was mildly abnormal at 1.42 (normal < 1.4) suggesting mild CTS. Mild flattening of median nerve was also noted at the carpal tunnel. The ulnar nerve was within normal limits on ultrasound examination.

Setting: Tertiary Medical Center, Outpatient

Assessment/Results: Patient underwent a right median nerve decompression at the LF and a right endoscopic carpal tunnel release with plastic surgery. Intraoperatively, the nerve at the LF was noted to be hyperemic and dilated. Occupational therapy evaluation done one-week post-op demonstrated full recovery of sensation and function in right hand.

Discussion (relevance): Lacertus syndrome can be evaluated on physical exam with Tinel’s over the LF, as well as FPL weakness. Abnormal ultrasound findings include increased CSA at the LF, visible focal entrapment, and/or Tinel’s present on sonopalpation of the median nerve at the LF.

Conclusions: Lacertus syndrome should be included in the differential diagnosis of median nerve entrapments and evaluated for on physical and ultrasound examination.