There are few reports documenting the presence of melanin or melanocytes in
epidermal cysts. One hundred and twenty five epidermal cysts from Indian p
atients were analyzed for the presence of melanin pigment and their sites w
ere noted. A Masson's Fontana stain and inummohistochemistry for S-100 prot
ein and HMB 45 was performed for localization of melanin and melanocytes wi
thin the epidermal cysts.
Seventy-nine (63%) of the epidermal cysts showed presence of melanin pigmen
t or melanocytes to a variable extent. Melanin was not present in epidermal
cysts occurring along lines of fusion of skin folds during embryonogenesis
(e.g., ventral midline, inner canthus, nose, upper lip and in the distal m
ost parts like leg and foot and also scrotum). Ten of the 79 epidermal cyst
s showed extensive accumulation of melanin pigment and infiltration with me
lanophages in the cyst wall. Four of these patients gave history of trauma
and the follow-up was uneventful in two of them.
Pigmentation of epidermal cysts thus follows a definite anatomic pattern an
d is dependent on the natural skin color. Large amount of pigment accumulat
ion within epidermal cysts occurs after cyst rupture and is not associated
with hemochromatosis as was believed in the past.