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psoriatic arthritis ( psa ) is a chronic inflammatory disease characterized by the association of arthritis and psoriasis .
psa is one of the subsets of seronegative arthropathies that share clinical features , including asymmetrical and oligoarticular joint involvement , a similar incidence in men and women , the same occurrence rate of dactylitis and enthesitis , negative rheumatoid factor and anti - cyclic - citrullinated - peptide antibody , and extra - articular manifestations such as onychitis and iritis .
the spectrum of joint inflammation in psa is wide , ranging from axial to peripheral disease , synovial and adjacent soft tissue inflammation , enthesitis , osteitis , new bone formation and severe osteolysis , and overlaps of all of these . in comparison with rheumatoid arthritis ( ra )
furthermore , bone proliferation is more common and tenosynovitis is less frequent in psa than in ra .
psoriatic onycho - pachydermo - periostitis ( popp ) is considered a rare form of psa , which is extremely painful and debilitating .
the first step for a successful treatment is to recognize popp as a manifestation of psa and to treat the disease with immunosuppressive therapy as soon as possible .
a 53-year - old construction worker , suffering from slight palmo - plantar psoriasis for many years , came to our attention for the sudden onset ( 2 months ) of onychodistrophy , onycholysis , and swollen painful hands and feet digits .
he had been treated by his medician for at least 2 months with topical antibiotics for bacterial perionyxis .
then , he went to a dermatologist who gave him other topical treatments and oral therapy for the pain for weeks .
when he arrived at our department , clinically he presented erythematous and desquamative lesions in his feet and hands , associated with erosions and rhagades [ figure 1 ] .
lesions of the soles appeared well demarcated by an erythematous peripheral ring [ figure 2 ] .
dystrophy of the nails was characterized by abnormal hyperkeratosis which made them similar to ostraceous shells [ figure 1a ] .
feet rx showed enthesitis and slight erosions of the terminal phalanges , with narrowed intra - articular spaces .
magnetic resonance imaging ( mri ) of the hands showed extensive synovitis and periostitis of the distal phalangeal tufts .
laboratory investigation did not show any abnormality and rheumatoid factor was negative . considering the clinical data such as association with psoriasis , painful enthesitis - synovitis , nail damage and negative rheumatoid factor
the patient was treated with methotrexate ( 12.5 mg per os / week ) for 21 days with a brilliant resolution of the lesions and symptoms [ figure 3 ] ; then , methotrexate dosage was slowly decreased ( 2.5 mg every 2 months ) .
now , the patient is under a maintenance dosage ( 2.5 mg / week ) in order to avoid relapses .
hyperkeratosis and onycholysis of hands , fingers with soft tissue swelling of the terminal phalanx .
dystrophy of nails is similar to that of the hands methotrexate treatment improved the patient 's onycholysis and painful erythematous swelling of the terminal phalanx .
it is characterized by onycodistrophy , onycolysis , connective tissue thickening above the distal phalanx and periosteal reaction leading to deformity of the digits .
a possible pathogenetic mechanism could be an inflammation starting from subungueal structures and spreading between tendons and bones of the terminal phalanx .
a hypothesis is that enthesitis arises at sites of high shear and compression forces , with the additive interaction between mechanical stress , microtrauma , tissue repair mechanism and bacterial molecules , variably leading to inflammation .
this model could suggest a possible explanation for the observation that psa ( and secondly popp ) may be associated occasionally with a preceding joint injury .
further , there may be a link to the skin component as injury to the skin is known to be a factor in expression of psoriasis . considering popp , the possible clinical differential diagnosis includes ungueal mycosis , reiter 's syndrome , hallopeau syndrome , bazex acrokeratosis .
most important differential diagnoses are for dermatophytosis that can show a very similar clinical manifestation and candida infection characterized by painful paronychia . in our case
, we could easily exclude this infection because of the negative mycological microscopic and cultural examination . in reiter 's syndrome , involvement of nails
is very similar to that in popp , but this syndrome is a genetically determined , often protracted host response to specific preceding enteric or genitourinary infection .
it is usually characterized by an abruptly appearing , reactive , asymmetric inflammation of the synovium and periarticular tissue , accompanied by mucocutaneous , ophthalmic and genitourinary involvement .
hallopeau acrodermatitis is a sterile pustular eruption of the fingers , which slowly extends proximally .
final stages of this disease could be similar to that of popp lesions , but popp has no pustular lesions , and nail changes are characterized by hyperkeratosis rather than dystrophy or onycholysis .
we could exclude bazex acrokeratosis because of the localization of the lesions to hands and feet ( bazex syndrome usually also involves ears , nose , cheeks , elbows and knees ) .
furthermore , bazex syndrome is associated with neoplasia of the upper respiratory tract , while our patient was in a good health condition . in ra , excessive ridging and sometimes beading of the nails
when ra is associated with psoriasis , any of the nail changes found in the latter disease may be present .
popp diagnosis is made by x - ray examinations , ultrasonography ( us ) and mri , with mri being considered as the golden standard .
both us and mri are more sensitive for visualization of inflammatory and destructive changes in patients fingers and toes because they have a major potential for improved examination of joints , tendons , and entheses in fingers and toes of patients with psa .
treatment for popp is not standardized ; mainly , the medications commonly used for psa .
popp is usually treated with low - dose methotrexate or anti - tumor necrosis factor ( anti - tnf ) medications , although methotrexate 's traditional role as a first - line agent for moderate to severe psoriasis is being challenged by the rapid growth and use of biological therapies .
nowadays , the question remains whether most biological therapies have superior efficacy than the traditional systemic agents such as methotrexate in a short time .
however , the significant cost differential and the current lack of long - term safety data for biological agents means that drugs such as methotrexate are likely to remain one of the first - line choices for the future treatment of psa localized forms ( and therefore for popp ) . considering that our patient had never been treated for psoriasis and the lesions
were limited to hands and feet , we started therapy with methotrexate rather then biological therapy .
the rapid resolution , either of the clinical lesions or the pain , confirms that popp should be recognized as a specific entity in the spectrum of psa , as shown by other similar cases in literature . in view of popp being considered as a subtype of psa , it is easy to understand that not only immunosuppressive treatment is useful but also it is mandatory to stop disease progression that could otherwise lead to severe and destructive arthritis .
so , finally , we underline the importance of an accurate and rapid diagnosis and an immediated therapy of popp disease , which is a subset of psa with a rapid evolution that can be easily mistaken even by specialists .
psoriatic onycho - pachydermo - periostitis ( popp ) is a rare subset of psoriatic arthritis . 
 it is usually localized to the hands and it is characterized by onychodistrophy , soft tissue thickening above the distal phalanx and periosteal reaction . 
 the resolution is very slow due to the involvement of nails and bone . 
 low dose methotrexate and anti - tumor necrosis factor- ( anti - tnf- ) agents are the suggested therapies . 
 we report a case of a 53-year - old man affected by palmo - plantar slight psoriatic dermatitis , who presented a rapid onset of popp . 
 rx imaging showed enthesitis and a moderate phalanx erosion with articular spaces narrowing and swollen periosteal reaction . 
 a magnetic resonance imaging test of the hands showed an initial stage of synovitis and extensive periostitis of the distal phalangeal tufts . 
 the patient has been treated with oral methotrexate for a month with a rapid clinical improvement and pain reduction . as popp at first manifests as a painful onycodistrophy 
 , it can easily be confused with bacterial perionyxis . the delay in making the correct diagnosis , and 
 therefore , the delay in giving a proper treatment would mean the progressive articular erosion and the permanent invalidation of the patient 's ability to use his hands .