Pathology of Colloid Milium
Colloid milium is an unusual cutaneous disorder characterized by multiple cystic papules.
It is a degenerative process in which the papules are located on the photoexposed areas.
The material in the dermis represent a degeneration product of elastic fibers which is induced by solar radiation.
Colloid milium and colloid degeneration include at least four distinct clinicopathological conditions:
- Classic adult type colloid milium
- Juvenile colloid milium
- Pigmented colloid milium (hydroquinone related)
- Colloid degeneration (paracolloid)
Classic adult type colloid milium :
- The adult form develops in sun-exposed parts of the body in patients who have actinic-damaged skin.
- Develops in mid-adult life.
- Plenty of yellow-brown, semitranslucent papules or plaques (1 to 4 mm in diameter) are seen in the cheeks, ears, neck, and dorsum of the hands.
- Predisposing factors are exposure to petroleum products and/or excessive sun sunlight.
Juvenile type colloid milium :
- Exceedingly rare and develop prior to puberty.
- Papules or plaques are seen on the face and neck.
- Some cases are probably examples of erythropoietic protoporphyria.
Pigmented type colloid milium :
- Gray to black papules on the face, following the excessive use of hydroquinone bleaching cream.
Colloid degeneration :
- Nodules or plaque-like areas, on the face and is probably a heterogeneous group.
Adult form: Histopathology images above:
- Nodular masses of homogeneous, eosinophilic material expanding the papillary dermis and extending into the mid dermis.
- Fissure and cleft divide this material into smaller islands and fibroblasts are commonly aligned along the line of fissuring.
- A thin grenz zone of normal collagen, often with elastic fibers (which are also present between and below the colloid masses), separates the colloid material from the thinned overlying epidermis.
- Colloid material may be stained positively with crystal violet and Congo red and fluorescence with thioflavin T (better result on frozen sections).
- Absence of laminin or type IV collagen differentiates colloid milium from lipoid proteinosis and primary cutaneous amyloidosis.
- In most areas grenz zone is absent and basal layer may show hyalinization with a transition towards the dermal material.
- The colloid is PAS positive and sometimes, methyl violet positive but it is usually Congo red negative.
- Lightly pigmented colloid islands are seen in the upper dermis.
Colloid degeneration (paracolloid):
- Amorphous, homogenized dermal collagen with less conspicuous clefts, extends deeply into the dermis.
- The material is relatively acellular, weakly PAS positive but negative with Congo red and crystal violet.
Copyright © 2019 histopathology-india.net