Parapsoriasis

Question 1

What is parapsoriasis?

Answer 1

Dermatoses characterised by chronic, asymptomatic, erythematous scaly patches primarily on the limbs and trunk

Histologically these patches have a a varibale CD4+ T cell infiltrate (without atypia / features of MF)

Question 2

What are the clinical features of small plaque parapsoriais?

Answer 2

• Chronic small patches - round to oval - that are generally <5cm in diameter
• Erythematous (but less intense than psoriasis)
• Some have a yellow hue
• Fine Scale
• Generally asymptomatic
• can be mildly pruritic
• Either widespread or favour sun protected sites

NB: A distinct and perhaps the most typical presentation is “digitate dermatosis”, which presents as elongated, finger-like patches symmetrically distributed on the flanks

Question 3

What are the histological features of small plaque parasporiasis?

Answer 3

• Mild, nonspecific spongiotic dermatitis with focal parakeratosis.
• Sparse lymphoid infiltrates within the superficial dermis
• with variable exocytosis into the epidermis
• composed primarily of CD4+ T cells
• no atypical T Cells, no pautriers micro abscesses

In most patients, molecular genetic studies demonstrate an oligoclonal or pseudo-monoclonal pattern
○ T cell clonality is demonstrable in some cases

Question 4

What is the DDx of small plaque parapsoriasis?

Answer 4

• Pit Rosea
• Drug eruption
• PLC
• Psoriasis
• MF
• Syphillus
• Nummular dermatitis

Other ‘papulosquamous disorders’

Question 5

Who does small plaque parapsoriasis effect?

Answer 5

• Middle aged and elderly, but can occur in children
• Peaks in the 5th decade (40s)
• Male predominance (3:1)

Question 6

How is small plaque parapsoriasis treated?

Answer 6

• Topical corticosteroids (mid - high potency)
• Natural sunlight
• NbUVB
• PUVA
• UVA1 phototherapy
• Antihistamines

Question 7

What is large plaque parasporiasis?

Answer 7

Controversial, many authors believe it is early MF

Similar clinical features, distrubution and histology.