Objective: Abnormal lymphatic function defined by scintigraphy in hand transplant patients has been reported. In cases of chronic edema, it is not clear whether swelling is due to inadequate lymphatic function, vascular leakage, or both. In hand transplantation, deep lymphatic vessels are not anastomosed. Surface lymphatic drainage reestablishes spontaneously. Feasibility of upper limb lymphatic infrared imaging with indocyanine green (ICG) has been demonstrated in breast cancer patients. However, there is no body of information on objective measurement of lymphatic function with ICG using normal controls. During pilot scans of our transplant recipients, it became clear that we had to define normal subcutaneous ICG clearance before we could define abnormal function. The aim of this study is to establish parameters of lymphatic function defined by clearance of subcutaneous injection of ICG in normal controls. The ultimate goal is to noninvasively define adequate and inadequate lymphatic function in hand transplant and replant patients. Methods: After obtaining institutional review board approval (IRB) approval, we enrolled 10 (age range, 23-54; 5 males and 5 females) normal controls. Patients with a history of allergy to iodine or shellfish were excluded. Hand transplant recipients were imaged initially using a dose of 0.25 mg of ICG. Subsequently, dose titration studies were performed in normal controls. Doses ranged from 0.25 mg to 0.025 µg of dye per subcutaneous injection site on the volar or dorsal side of the hand in 100 µL of saline. The stock vial of ICG is reconstituted with sterile water per manufacturer’s (Novodaq, Novadaq Technologies Inc, Ontario, Canada) instructions. Subject hand and upper extremity was then imaged using the LUNA Florescence Angiography unit at 15 minutes to hourly intervals up to 6 hours postinjection. Selected patients were also imaged every 24 hours until dye cleared completely from the injection site. Images were analyzed using SPYi software. Results: Injection of 2 sites on the dorsal, but not volar side of the hand, allows clear visualization of drainage of ICG by both ulnar and radial lymphatic vessels from the hand to the antecubital fossa and the arm in the brachial veins. Relatively low doses of dye allow excellent visualization. In normal controls, ICG can be visualized in the antecubital fossa in a linear pattern by 15 minutes and in significant amounts by 30 minutes. Higher doses of dye were associated with excessive retention of dye at injection site with no improvement in vessel visualization. Hand transplant recipients demonstrated a mixture of linear and radial drainage, with more involvement of small superficial capillary-like networks. Conclusions: These pilot studies show that subcutaneous clearance of ICG as a targeted near-infrared (NIR) molecular imaging agent can be used to define lymphatic function. By combining subcutaneous injection with intravenous imaging of ICG, we hypothesize that the role of lymphatic function versus vessel leakage in chronic edema can be differentiated. Further studies are needed to identify whether this could be helpful in the evaluation/treatment of patients with lymphostasis related to burns, cellulitis, other infections, and compartment syndrome.
