Pigmented lesion on neck.

A 57 year-old-woman consulted for a pigmented lesion on her neck.

Dermoscopy revealed:

• no melanocytic structures
• a structureless pattern
• irregular blue gray dots/globules 

Pathology was in favor of a Bowen's disease.

Homogeneous blue pattern

A 65-year-old man presented 6 blue lesions located on his trunk. Dermoscopy revealed a blue structure-less pattern (homogeneous blue pattern).
This patient had been treated 10 years before for a leukaemia. These blue lesions with blue homogeneous patterns not well demarcated corresponded to radiotherapy tattoos.

Radiotherapy tattoo

Radiotherapy tattoo

The main other cause of blue homogeneous pattern is blue nevus.
Here are above two examples of blue nevi.

Blue nevus

Blue nevus

Polychromous blue nevus

A 37-year-old woman consulted for a pigmented lesion on her left leg. The lesion was excised and pathology revealed a blue nevus.
Blue nevi are typically described as tumors showing steel-blue pigmentation with an homogeneous or structureless pattern. In fact blue nevi are not always blue on dermoscopy and these nevi have sometimes areas of discoloration, some of them can be tan (brown blue nevi) or variegated (polychromous blue nevi)