Multiple erythematous annular lesions with peripheral collorette of scales arranged predominantly on trunk are seen in –
PITYRIASIS

The term pityriasis is used to describe skin condition in which the scale appears similar to bran. So, any skin disease with pityriasis in its name will be scaly.

Differential diagnosis of different Pitriasis
Pityriasis rosea


Children and young adults
Erythmatous annular plaque → Mother patch (Herald patch)
Mainly involves Trunk.
Christmas tree or Fir tree configration
Collarette scales (cigar paper scale)
Self limiting course

Pityriasis rubra pilaris

Two peaks → 5-10 years and 40-60 years
Elythmatous (orange to pink), follicular, scaly plaques
Characteristic presence of distinct island of normal skin
Involvement of trunk with cranio caudal distribution
Nutmeg papules on knuckles
Thickening of palms (Palmer thickening) & soles (keratoden-nic sandals)

Pityriasis lichenoides
1)   Pityriasis lichenoides et variolifermis acuta

Constitutional symptoms; fever, arthralgia
Multiple erythmatous & edematous papules often surmounted by vesicles
Lesions heal with hyperpigmented scar 
Trunk and flexures of arm

2) Pityriasis lichenoides chronica

Successive crops of red-brown papules which are surmounted by a central adherent mica like scales
Lesions heal with hypopigmentation
Trunk and proximal part of extremities

Pityriasis alba

Children (6-12 years)
Hypopigmented macule on face
Presence of fine scales

Pityriasis versicolor

Young adults
Hypopigmented macule
Fine scales → Furfuraceous or rice powder like scales
Involvement of Trunk and shoulder (chest & backs)

Note - Pityriasis Rosea, Pityriasis rubra pilaris and pityriasis lichenoides are papulosquamous lesions, whereas pityriasis versicolor and pityriasis alba are not papulosquamous lesions.
Pityriasis vesicular
Pytiriasis rubra pilaris
Pityriasis rosea
Pityriasis lichennoides chronica