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Granuloma Annulare

Author: Chris Hallam 

Chief Editor: Dr Daniel Keith

Granuloma annulare (GA) is a relatively common skin condition that can affect people of all ages, though it mainly affects children and young adults. The exact cause of GA is unknown. While it can appear in different forms, the typical presentation is a smooth, annular plaque with a papular edge. On histology, it shows areas of collagen degeneration surrounded by granulomatous inflammation.

Macroscopic Appearance 

  • Typified clinically by annular, smooth, discoloured papules and plaques.

  • Generalised GA presents as widespread skin-coloured, pinkish or slightly mauve-coloured patches.

  • Disseminated GA presents as small papules, usually arranged symmetrically in poorly defined rings (≥10cm in diameter).

  • Annular rings may be solitary or multiple and grow outwards maintaining the ring shape before eventually clearing.

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Dermoscopic Appearance 

The dermoscopic features of granuloma annulare are heterogeneous and vary according to the histopathological subtype. The vascular changes are relatively subtle in comparison to those typically seen in other granulomatous conditions. Consistent findings include the presence of unfocussed vasculature on a pink to reddish background, with variable morphology – commonly dotted, linear-irregular, or branching patterns.

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Nonvascular findings:

  • Whitish discoloration and structureless yellow-orange areas (can be focal or diffuse)

 

Vascular findings:

  • Unfocused vasculature on a pink to reddish background

 

Others:

  • Pigmentation, rosette shapes, crystalline leaf venations

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The whitish areas and yellow-orange structureless regions correspond to underlying changes seen on histology. These changes include collagen degeneration, mucin deposition, dermal fibrosis, and dermal granuloma formation.

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