Palmoplantar pustulosis (PPP) is a chronic and relapsing disease of the palms and soles, which is characterized by scattered clusters of pinhead-sized, sterile pustules, primarily located on the thenar, hypothenar, or central areas of the palms, either in a symmetrical or asymmetrical fashion (Fig. 1). Although initially thought to be a variant of psoriasis,1 PPP is now regarded as a separate entity rather than a disease on the psoriasis spectrum.2,3 Despite the fact that some patients have psoriasiform plaques on other parts of the body, these lesions are not considered as the typical psoriatic plaques.4 Eccrine sweat glands and the acrosyringium play the central role in the pathogenesis of PPP.5,6 PPP is a disease with female predominance. There is also a well-recognized association with smoking.1,7 In addition, some reports notify that abnormality in thyroid functions7,8 and contact sensitivity9 are associated with PPP. The aim of the present study was to determine demographic features, the frequency of thyroid autoimmunity, contact sensitivity, concomitant arthritis, nail involvement, and the presence of psoriatic lesions on dermatological examination in patients with PPP.

Figure 1.

Pustules located on normal and erythematous skin of palms with brown discoloration.

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A cross-sectional observational study was conducted. A total of 48 consecutive patients (15 men and 33 women) who were diagnosed with PPP between January 2014 and January 2018 and met inclusion criteria were enrolled in the present study.

The study was conducted according to the principles of the Declaration of Helsinki and approved by the local ethics committee. Written informed consent was obtained from all the participants before study inclusion. Study inclusion criteria were as follows: age≥18 years and voluntarily agreeing to participate in the study. Occupational exposures of participants as well as demographical and clinical characteristics were recorded, including age of onset, duration of PPP, the number of recurrences, personal and family history of psoriasis, presence of psoriatic lesions at the time of data collection, accompanying arthritis and/or sternoclavicular joint tenderness, presence of dental filling, smoking habits, and autoimmune disease history. For each patient, a thorough dermatological examination was carried out. In particular, patients were carefully examined to detect concurrent psoriatic lesions in the rest of the body. Patch testing results and laboratory investigations for thyroid autoimmunity were recorded.

PPP affects mostly females and the age of disease onset ranges from 45 to 65.1,3 Lesions are often accompanied by desquamation and brown discoloration during regression (Fig. 2). Recurrences and spontaneous remissions are common. Pustules can be located on normal or erythematous skin. Absence of any of psoriatic plaques, pustules located on areas other than palmoplantar region, and/or erythroderma or lack of personal/family history of psoriasis are the characteristic features of the disease. Patients who enrolled in the present study had neither classic plaque psoriasis lesions nor personal or family history of psoriasis. It has been suggested that PPP is an autoimmune disease triggered by nicotine7,8; however, it is well known that smoking cessation does not always have a favorable effect on disease progression. In the present study, a significant ratio of patients had an active or previous history of smoking. However, 11 of 48 patients had no active or passive exposure to tobacco smoke.

Figure 2.

Desquamation and brown discoloration on erythematous skin of palms.

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Although PPP has been linked with psoriasis and psoriatic lesions located on body areas other than the palms and soles,1 it has been reported that these lesions actually were linked to psoriasis incorrectly; indeed, these psoriasiform lesions do not resemble classic psoriatic plaques.4 Currently, it is well known that psoriasis and PPP are almost separate entities with respect to cytokine profiles, clinical findings, and genetic susceptibility.12,13

Nail involvement – including pitting, onycholysis, and dystrophy – can be detected in patients with PPP.1,14 Seven of the present patients (14%) had onycholysis unrelated with onychomycosis; in additions, three of the seven also had pitting.

Smoking and thyroid gland dysfunction are the coexisting conditions most often investigated in patients diagnosed with PPP, and the association between tobacco use and PPP is well established.1,15 The present study also found a considerable ratio of smoking, particularly in male patients. Thyroid gland dysfunction, including autoimmune thyroiditis, has been reported in many clinical studies.1,16 The present study detected autoimmune thyroid disease in four of 48 patients as elevated anti-thyroid peroxidase antibodies, low levels of free-T4, and ultrasonographic findings of Hashimoto's thyroiditis.

Based on the report suggesting spontaneous regression of PPP after removal of dental amalgam,9 all patients were questioned for presence of dental fillings. There was no significant correlation between duration of PPP and duration of dental filling (p=0.170). Out of the 11 patients who had dental filling, two patients showed patch test positivity to nickel sulfate. Based on these results, it is difficult to say that there is a contact sensitivity resulting from amalgam in the dental filling. Published reports indicate associations of PPP with arthralgia predominantly located in the hands and fingers,16 psoriatic arthropathy,17 and pustulotic arthro-osteitis (Sonozaki syndrome).18 However, some findings from these studies are debatable. For example, in the retrospective study of Becher et al.17 in which psoriatic arthropathy was reported in 12.3% of patients, a significant proportion of patients had family history of plaque psoriasis or concurrent plaque psoriasis. For this reason it is difficult to conclude there is a link between psoriatic arthropathy and PPP. Sternocostoclavicular hyperostosis (SCCH), which presents with swelling and pain of the sternoclavicular joint, was reported firstly in a Japanese patient with PPP. After this case report, Sonozaki termed this clinical entity as pustulotic arthro-osteitis (Sonozaki syndrome, PAO).19 Due to frequent association between PPP and pustulotic arthro-osteitis, they suggested that SCCH might be a musculoskeletal manifestation of PPP. In the present study none of the patients with PPP had clinical findings or history of SCCH.

It is well known that psoriatic nail disease, especially crumbling and onycholysis, are related with susceptibility to distal interphalangeal (DIP) arthritis in patients with psoriasis.20 One of the present patients who suffered from arthralgia in the small joints of the hands also had onycholysis, but she did not have objective clinical findings of DIP arthritis. In this context, the authors believe that nail and joint involvement should be evaluated among PPP patients in future studies with larger sample size.

Positivity of patch testing with allergens, especially with metals, was reported in PPP patients. In these case reports, positivity of patch testing is correlated with dental fillings including nickel, cobalt, and zinc.9,21,22 Removal of dental fillings led to the regression of PPP lesions in sporadic case reports.9 It is always important to relate patch testing results to history and clinical findings. It is difficult to say one of the etiopathogenic factors for PPP is systemic contact sensitivity because of the lack of large case-control studies. In the present series, two patients had both nickel positivity and dental fillings; however, the duration of dental filling was not compatible with PPP disease duration.

Some findings of the present study – including female predominance, high prevalence of smoking habits, and nail involvement – are compatible with the literature. Based on the increasing evidence and the data presented here, PPP appears to be a distinct entity from psoriasis. Of note, the available studies clinically describing PPP are limited and controversial. The present study did not find a correlation between PPP and psoriasis. According to these results, the triggering role of contact sensitivity in the etiopathogenesis of PPP is unclear and patch testing may not be required in patients with PPP. Routine thyroid function tests could be analyzed in patients diagnosed with PPP due to the high prevalence of thyroid function abnormality in patients with PPP. Also, patients with PPP must be evaluated for musculoskeletal signs and symptoms. It is unclear whether typical PPP is associated with psoriatic arthritis or any other inflammatory arthropathies. In order to clarify this, arthritic symptoms should be investigated in large patients groups.

None declared.

Ayse Oktem: Approval of the final version of the manuscript; elaboration and writing of the manuscript; effective participation in research orientation; critical review of the literature.

Pınar Incel Uysal: Statistical analysis; effective participation in research orientation.

Neslihan Akdoğan: Conception and planning of the study; critical review of the literature.

Aslı Tokmak: Elaboration and writing of the manuscript; obtaining, analyzing, and interpreting the data.

Basak Yalcin: Approval of the final version of the manuscript; critical review of the manuscript.

None declared.