Collodion baby and lamellar ichthyosis.

It is important to differentiate the collodion baby from harlequin ichthyosis as the latter rarely survives past the first few days of life. Occasionally, babies share features of both disorders and defy a clinical diagnosis. We recently encountered such a baby who initially presented with harlequin-like features, but evolved into lamellar ichthyosis once the keratin cast was shed. Since the routine histology of all these ichthyoses is similar, we used electron microscopy to study serial biopsy specimens from the affected infant on days 7, 14, and 150, and compared them to our own other cases of harlequin ichthyosis and lamellar ichthyosis. Electron microscopic studies of our case revealed that the marginal band of cornified cells of the stratum corneum was absent when the baby exhibited collodion/harlequin ichthyosis features. Another biopsy taken when the clinical picture evolved into lamellar-like ichthyosis, showed a well-formed marginal band in the cornified cells. In harlequin ichthyosis, the marginal band is present at birth. It is suggested that electron microscopy can differentiate severe collodion baby from harlequin ichthyosis at birth using the absence of the marginal band. Previously reported features of harlequin ichthyosis, such as the presence of giant mitochondria and an abnormal formation of the marginal band in luminal villi of acrosyringeal eccrine duct, were absent in our case.