Dysfunction of dermal initial lymphatics of the arm and upper body quadrant causes congenital arm lymphedema.

OBJECTIVE: The objective of this study was to explore the pathologic process underlying primary lymphedema.

METHODS: Twenty-seven patients with unilateral congenital arm lymphedema who visited our clinic from January 1, 2014, to May 30, 2019, were enrolled. The patients' clinical signs and the findings of indocyanine green (ICG) lymphography, skin tissue immunohistochemical staining, and whole exome sequencing of tissue and blood were evaluated.

RESULTS: Among the 27 patients, 11 were diagnosed with stage II and 16 were diagnosed with stage III lymphedema. No lymphatic vessels were visualized in the affected arm in 25 of 27 (93%) patients who underwent ICG lymphography; likewise, no lymphatics were found in the territories of axillary lymph node drainage in the trunk, irrespective of any anomalies of the axillary lymph nodes. In only two (7%) patients, an unclear lymphatic trunk gradually appeared in the dorsum of the affected hand. The number of initial lymphatics was increased in the skin specimens of all nine patients in whom lymphatics were not demonstrated by ICG lymphography. Among 14 tested patients, we found compound heterozygote variants in the PIEZO1 gene in only one (7%) patient. Two missense variants, c.4072C>T; p.Arg1358Cys and c.5033C>T; p. Ala1678Val, were identified and found to have been inherited from the father and mother, respectively. No other pathogenic or likely pathogenic variants of currently known lymphedema-related genes were identified in the remaining 13 patients. No genetic difference was found between the lymphedematous and nonedematous healthy skin tissue of the same person.

CONCLUSIONS: Segmental or regional dysfunction of the dermal initial lymphatics causes congenital arm lymphedema and may have implications for clinical treatment.