Primary morphological elements

Primary morphologic elements (from Greek morphe – form and logos – teaching) are the basic clinical manifestations of skin diseases that appear on unchanged (healthy) skin. It is with the appearance of these elements that any dermatosis begins.

Correctly identifying the type of primary element (spot, nodule, vesicle, etc.) is key to making the correct dermatologic diagnosis.

Classification

All primary elements fall into two large groups:

• Cavitary: Have a cavity inside filled with contents (serous, hemorrhagic, or purulent). These include: vesicle, bubble, pustule.
• Cavityless (infiltrative): Have no cavity, present as a discoloration or cluster of cells in the layers of the skin. They include: spot, papule, nodule, blister, and bump.

Clinical significance

The evolution (development) of primary elements leads to the appearance of secondary elements (crusts, erosions, ulcers, scars). The dermatologist always seeks to find the primary element, as secondary changes are often less specific and may mask the true cause of the disease.