Psoriasis

The lesions

Typical lesions  are red raised and scaly  and have well- demarcated margins fig11.1] .The  scaling is often silvery or thick and like  candle grease plaques  vary enormously  in size  and shape .They  often  start out  discoid , but end  up  polycylic fig 11.2] as several  lesions coalesce.

Site  affected

Psoriasis affect the extensor  aspect of  the trunk  and limbs preferentially the knees  elbows and scalp  are especially frequently  affected  Fig 11.3]., although the mucosae seem  to be spared.the  nails  are often  affected  and may  show the  so- called  thimble pitting separation  of the nail plate from the  nail bed [Onycholysis].  Subungal    debris  brownish – black  dis colorations  and deformities  of the  nail  plate  [ Fig 11.4].

Flexural lesions which occur in some  patient are most  often seen in the major body folds in the elderly  especially in those  who are overweight.The groins  and genitalia, axillae,  inframammary  folds in women  and the skin  of abdominal folds and the  umbilicus  in either sex  are affected .The  moistness  of the  flexural  areas  decreases the scaling and produces  a moist  and  glazed  appearance  [Fig 11.5]. The  face is not often  involved  in  Psoriasis and when  it  is it is  not usually  severely  affected  . However  the scalp  margin , paranasal folds  and retroauricular  folds are quite  often  involved [Fig 11.6]

Genetics

Psoriasis is often  familial , but does not  appear to be inherited  in anyregular dominant sex- linked  or recessive  way. With  one parent  affected ,  there  is an  approximately 30 percent chance  of  a child being  affected . With both parent  suffering    from Psoriasis, the chance that  a child  will develop  the condition  rises to 60 per cent .In  a recent  survey  in Sweden , it    was found  that  6.4 per cent  of relatives  of families in which  there was a patient  with Psoriasis were affected  compared  with 19.4  per cent   of controls  .  Non – identical  twins  have an  approximately  20 per cent  chance  of both  being affected  and  the  concordance  rate  for identical  twins  seems to be  in the order  of percent . Recent  research  indicated  that, although   no  one   gene  is responsible  for the   disease, the direct in heritance  of ‘susceptibility genes’   is necessary   for its  development . The  familial  clustering  noted  in type  I is  much less  evident  in  late – onset  Psoriasis .

Psoriasis is associated  with  human  leucocytle  antigen  [HLA] group  HLA­­­­­­- B13 ,  HLA –B17  and  HLA –B 37  as well as with  the class II  antigen  DR 7  it is even  more   strongly  associated  with CW 6 – increasing  the risk  of the  disease  some 13  time  in Caucasians .

C linical variants

Guttate psoriasis

This disorder is mainly  seen  in children aged 7-14 years  often  it develops  some 2- 4 weeks  after  an episode  of tonsillitis  or pharyngitis  mostly   due to  beta – haemolytic  streptococci  the disorder  behaves  like an  exanthem , as  the  characteristically  drop  – sized  lesions  develop  suddenly [ FIG11.10 ].  And  at  the  same time  . The  lesions  do not  usually  last long  fading  away  after 8 -10  weeks.

Napkin  Psoriasis

Infantile   napkin  dermatitis  sometime  take on   a very  psoriasis  like  appearance  and typical   psoriatic   lesions  develop on the scalp   and  trunk  the true relationship  with  psoriasis is unknown .

 Erythrodermic  Psoriasis

 Psoriasis  sometimes progress  to generalized  skin involvement .Typical  plaque –like  lesions  disappear , the skin  is uninersally  red and scaly  and the  condition is known  as  erythrodermic  psoriasis . these  patient , who  are  seriously  ill , suffer  from;

. HEAT loss and are  in danger  of hypothermia  because   of the  increased blood  supply  to the skin  and the  skin and the  subsequent  loss of the heat.

. water loss  leading  to dehydration  because  of the  disturbed barrier  function  of the  abnormal  stratum corneum .

. hyperdynamic   circulation ,  because  effectively  there  is a  vascular  shunt  in  the  skin when  the patient s myocardium is already   comparised  because  of other factor,  there  is a danger of high  output  cardiac  failure

. loss of  protein  electroyates  and metabolites  via the  shed  scale  and  exudates  patient  may develop  deficiency states.

Pustualar  Psoriasis

Most  dermatologists  consider  this  to be  a manifestation  of psoriasis  although  there are some   who believe it is a separate  disorder . It  seems  probable  that pustular  Psoriasis, with exaggerationof one particular  component of the disease [ see  pathology below] . There  are two main types

. palmoplantar  pustulosis

  Patient  with  palmoplantar   pustulosis  develop  yellowish  white,stertile pustules  on the central  parts  of the palms  and soles [FIG 11.1]   older  lesions  after 1-2week  take on  a brownish  appearances  and are later  shed  in a scaly  and  fissured  and although relatively  small  areas of skin  are affected  the condition  can be very disabling .

The disorder  tends  to be resistant  to treatment [ see  below] and is  subject to relapses  and remission  over many  year.  There  is avery  strong relationship between  this form of  Psoriasis and cigaraette smoking.

. Generalized  Pustular  Psoriasis

This  is also knowneponymously  as von  Zumbusch ‘s  disease  and is one of the  most potentially  serious  disorder  dealt  with by dermatologists . In  its  classic  form , attacks  occur   suddenly  and Are  characterized  by severe  systemtic  upset ,  a  swinging  pyrexia ,  arthralgia  and a  high  polymorphonuclear  leucocytosis  accompanying  the skin  disorder.

The skin  first  become  erythrodermic  and  then  develop  sheet of stertile pustules 2-4mm  in  diameter  over the  trunk  and limbs [Fig 11.13]sometimes , the pustules  become  confluent  so that ‘ lakes  of pus’ develop  just beneath  the skin  surface . In  other  areas  there  is a curious  types of  superficial  peeling  without  pustules  forming .

These  patient  are very  unwell  and require  hospitalization .They can  usually  be brought  into remisson  by  modern  treatment [see below] , but  are subject  to recurrent  attacks . The  disorder  sometimes  affect  infants  and small  children .

Other  form of  Pustular Psoriasis

Occasionally pustules  may develop  locally  after strong  topical corticosteroids  have been  used or become  widespread   after   systematic  corticosteroids have been  administered  and then  abruptly  withdraw . other  rare  variants of pustular psoriasis  include

. acrodermatitis  continua ,  in which  there is   a recalcitrant  pustular  erosive disorder  on the  finger  and toes  around the  end  of the  finger  and the nails  and occasionally  elsewhere.

. pustular  bacterid , in which  stertile  pustules  suddenly  appear  on the palms soles  and distal  parts  of the limbs  after an  infection .

.widespread  pustules  also occur  in the  condition  of  impetigo  herpetiformis , seen  in pregnancy and the disorder  known  as  subcorneal pustular  dermatosis

Arthropathic  Psoriasis

 There is a higher prevalence of a rheumatoid – like  arthritis  with symmetrical  involvement  of the small  joint  of the hand  and feet , wrists and ankles  in  patient with  psoriasis 5-6 per cent and some  aurthorities  claim  an even  greater  proportion  of people  with  psoriasis  are affected  compared  with a  matched  control population  1-2 percent ]. This  ‘rheumatoid  arthritis  – like ‘  disorder  differ  in one important respect  from ordinary  rheumatoid  arthritis – there is no circulating  rheumatoid  factor .

In  addition  there is  a distinctive and a nd destructive  from of joint  disease  that seems specific  to psoriasis  . In this ‘ psoriatic arthopathy’  . The  distal interphalangeal joint , the temporomandibular the sternomanubrial  and the  sacroiliac  joint are particulary  affected  . The disorder  is more  destructive than rheumatoid disease.  Bony  erosion  and destruction  take place ,leading  to    ‘collapse’   of affected   digit [ Fig 11.14]. justifying the  term  often  used  for this  dreadful  disease – arthritis  mutilans.

Treatment  may temporarily  improve  these joint  complaications  of psoriasis  but the  disorder  tends  to run  a progressive  course  subject  to remissions  andrelapses.

Aetiology

The  cause  of psoriasis  is unknown , despite  the enormous  research  effort  that has been  made in the past  four decades . various  hypotheses  have been  popular  at different  times.  Ones  very  obvious  abnormality  in psoriasis is the hyperplastic  epidermis  with  increased  mitotic  activity ,and one  line  of intense  investigation  was  directed  at the control  of epidermal  cell production  in this disease.  Attention   has  moved  away  from this possibility  in  recent   year  suggesting  that  the  increased   mitotic  activity  and epidermal  thickness  are secondary  phenomena , and  has  focused more  on the  inflammation  and possible  immunopathogenesis.