|Year : 2014 | Volume
| Issue : 1 | Page : 12-15
Parakeratosis pustulosa: A diagnostic conundrum
Vikram K Mahajan, Nitin Ranjan
Department of Dermatology, Venereology and Leprosy, Dr. R. P. Govt. Medical College, Kangra (Tanda), Himachal Pradesh, India
|Date of Web Publication||2-May-2014|
Vikram K Mahajan
Department of Dermatology, Venereology and Leprosy, Dr. R. P. Govt. Medical College, Kangra (Tanda) - 176 001, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
Parakeratosis pustulosa (PP) is not so rare an entity and remains under reported in the literature perhaps for the simple reason of mistaken identity. The literature on PP was reviewed for epidemiology, etiology, clinicopathologic features, differential diagnosis, clinical course, and the therapeutic measures described. A Medline search (PubMed, Google, IndMed) carried out on 30 December 2012 revealed only 10 reports under the heading "parakeratosis pustulosa"; three were in languages other than English. This chronic dermatosis is characterized by erythemato-squamous lesions affecting the periungual skin/nail unit in children aged ≤5 years, mostly females. Nails show pitting and cross-ridging of one or more digits especially of the fingers. Its etiology remains obscure, and onychomycosis, psoriasis or pustular psoriasis, and atopic or contact dermatitis affecting the nail are important differentials. Acrodermatitis continua of Hallopeau remains the most common misdiagnosis in these patients. Topical emollients remain the recommended treatment, while topical corticosteroids or tretinoin are needed for recalcitrant cases. Evaluation of this as a distinct entity having benign, self-limiting clinical course and good prognosis will save the patient from expensive therapy and unnecessary distress associated with other more mutilating pustular dermatoses affecting the nail unit.
Keywords: Acrodermatitis continua of Hallopeau, acropustulosis, onychodystrophy, onycholysis, pustular psoriasis
|How to cite this article:|
Mahajan VK, Ranjan N. Parakeratosis pustulosa: A diagnostic conundrum. Indian J Paediatr Dermatol 2014;15:12-5
| Introduction|| |
Parakeratosis pustulosa (PP; Syn: Hjorth-Sabouraud syndrome) is a chronic dermatosis characterized by erythemato-squamous lesions affecting periungual skin with pitting and cross-ridging of the nails of one or more digits, almost with exclusivity in females aged ≤5 years. It was first described by Brocq as "parakeratosis psoriasis formes," but the first report on PP appeared in 1931 under the nomenclature "Parakèratose microbiènne du boût des doigts." , However, Hjorth and Thomsen  are credited to bring forth this entity in English literature under the heading "parakeratosis pustulosa." However, it remains under reported in the literature perhaps for the simple reason of mistaken identity. Its treatment as well as status as an independent entity also remains unclear. In view of the foregoing, we feel that there is a strong need to delineate this rarely reported but not so uncommon disorder for accurate diagnosis and uniform documentation. In this communication, we briefly review the literature for a simplified clinical description of this clinically less-familiar disease to compare the features of other closely mimicking dermatoses and to propose the clinical criteria for diagnosis.
| Review of literature|| |
A Medline search (PubMed, Google, IndMed) carried out on 30 December 2012 revealed only 10 reports under the heading "parakeratosis pustulosa"; three were in the languages other than English. ,,,,,,,,, These were analyzed for epidemiology, etiology, clinicopathologic features, differential diagnosis, clinical course, and therapeutic measures described.
Its prevalence remains unknown as it is inadequately described, often overlooked or misdiagnosed as psoriasis, eczema, acrodermatitis continua, atopic or contact dermatitis, and perhaps remains under reported in the literature for the simple reason of this mistaken identity.
Its etiology remains obscure. Absence of PP in siblings/family members suggests that it is not genetically transmitted. It has often been related with psoriasis, chronic dry fissured eczematoid dermatitis, or onychomycosis. Hjorth and Thomsen  reviewed 91 cases and noted personal or family history of psoriasis in 12 and atopic dermatitis in 16 patients, while the search for fungus was futile in 20 out of 36 patients examined. In a long-term follow-up (1-9 years) of 20 patients, Tosti et al. observed psoriasis lesions over scalp, left dorsal foot, and inguinal folds, either at first presentation (three patients) or as subsequent development of psoriasis/pitting of nails (five patients). They could also confirm presence of atopic or contact dermatitis in six other patients. Pandhi et al. implicated thumb sucking as a causative factor. However, a benign clinical course, spontaneous remissions, and improvement with emollients alone in most patients suggest that PP is a distinct entity whose etiology remains obscure.
Much of the clinical profile of PP described by various authors is based on an elucidating review of 91 cases by Hjorth and Thomsen.  The disorder occurs almost exclusively in children aged ≤5 years and mostly affects young girls. Thumb or middle finger is affected more often than the toes. The lesions start close to the free end of the nail as few pustules or vesicles in about 25% cases, evolving into more eczematoid changes over the adjacent skin.  Pink or skin-colored and sharply delineated plaques are densely studded with scales [Figure 1]. In long-standing cases, peripheral collarets of scales may be seen. In most cases, only the tips of digits are affected and the skin changes may extend on to the nail folds or dorsal side of the digits. The distal nail plate shows onycholysis usually at the corner. Though uncommon, subungual hyperkeratosis, when occurs, rarely extends beyond 1-2 mm into the nail bed.  Thickening and/or pitting of nail are uncommon, but ridging is usual. The distal pulp may be normal or may show mild erythema and scaling. However, pain and itching are conspicuously absent.  Briefly, erythema and scaling of periungual skin are the predominant features while pustule formation may occur only in the beginning. Subungual hyperkeratosis results in lifting up of the nail plate from the nail bed causing deformity resembling onycholysis.
|Figure 1: Parakeratosis pustulosa in a 6-month-old child. Erythematous, sharply delineated plaque densely studded with thin scales is present predominantly over pulp of the digit and nail fold of the right thumb. Also note minimal onycholysis and no nail dystrophy/pitting|
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The diagnosis remains clinical and is made best by exclusion. The proposed clinical criteria [Table 1] will assist in making early clinical diagnosis and uniform documentation until its status as an independent entity or otherwise becomes clear. Histopathologic studies are sparse. Only three reports describe the histologic features similar to chronic eczema or psoriasis. ,, As early as 1974, de Dulanto et al. reported the histology of one case and observed hyperkeratosis, parakeratosis, pustules, acanthosis, mild exocytosis, papillomatosis, and polymorpholymphocytic infiltrates. Later, Avci et al. additionally noted many dyskeratotic cells in stratum spinosum. Pandhi et al. also described hyperkeratosis, parakeratosis, mild acanthosis, and papillomatosis with infiltrate around the dilated blood vessels. These histologic features of hyperkeratosis, parakeratosis, mild acanthosis, papillomatosis, and polymorpholymphocytic infiltrate described in a few cases are nonspecific or similar to those seen in psoriasis or chronic eczema, and may not be helpful in diagnosis. Routine laboratory investigations also have no significant abnormality. Most investigative workup recommended is largely for exclusion of other dermatoses.
PP needs to be differentiated from other dermatoses affecting the nail unit, such as psoriasis, acropustulosis (pustular psoriasis and acrodermatitis continua of Hallopeau), atopic or contact dermatitis, onychomycosis (dermatophytic/non-dermatophytic), and chronic (mostly candidal) paronychia. Differentiation of various pustular dermatoses affecting the nail unit is perhaps more important for better therapeutic outcome. Notably, psoriasis/pustular psoriasis and acrodermatitis continua of Hallopeau, which usually are more chronic and incapacitating than PP, may cause diagnostic confusion. Important differentiating features of these are listed in [Table 2]. Acrodermatitis continua of Hallopeau sometimes can be very aggressive resulting in resorptive osteolysis of digits, but is mostly less mutilating than pustular psoriasis of the nail unit which is a more destructive form of acropustulosis that may cause nail loss in the long term.  In contrast, pustules are rare and transient in PP and seen in the initial stages only. Development of sheets of coarse scales is seen more with psoriasis-associated PP-like lesions.  Presence of psoriasis lesions elsewhere on the body in such cases will help in the diagnosis and must be looked for. Fungal infections affecting the nail units, however, need not be confused with PP and should be excluded by KOH preparation, fungal culture, and/or biopsy with special stains for fungus. Chronic paronychia mostly affects adults who are diabetic or whose hands are exposed to wet work (housewives, dish washers, bar tenders, laundry or canteen workers). The involved nails show loss of cuticle, erythematous, swollen, and mildly tender nail folds, and pus formation underneath. Nail discoloration and dystrophy is frequent in long-standing cases. Atopic or contact dermatitis can be diagnosed clinically (itchy, oozing lesions) or by patch testing with suspected allergens, respectively. Moreover, pustulation is not a regular feature here, not even a transient one.
|Table 2: Comparative features of parakeratosis pustulosa and other pustular dermatoses affecting the nail unit|
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Management and Prognosis
No specific therapy has been recommended. Though topical corticosteroids have been used in most reports, topical emollients remain the recommended mode of treatment. Few patients may need treatment with topical tretinoin. It has a benign and non-mutilating clinical course and prognosis is good. The onset is insidious and it usually regresses as the child grows up. A prolonged clinical course is often marked with spontaneous but unpredictable remissions, while recurrences are the rule. Children who develop nail psoriasis during clinical course perhaps had acrodermatitis continua/psoriasis in the beginning.
Its treatment as well as status as an independent entity remains unclear. According to Richert and Andre,  PP evolves toward complete healing within a few months/years without any sequelae or frank psoriasis in some patients. However, it may be appropriate to agree to the opinion of Tosti et al. that the definite diagnosis of PP is based on the location and features of the nail abnormalities that make the nail symptoms very distinctive, and finally should rest upon dermatological evaluation, patch testing, and long-term follow-up, i.e. exclusion of other dermatoses affecting the nail unit (vide supra). Acrodermatitis continua of Hallopeau is the most common disorder mistaken for PP as is evident from the images accompanying some published reports. For instance, the patient described by Park et al. who had spontaneous nail loss, erythematous scaly patch with pustule formation, and clearance with systemic etretinate appears to be of acrodermatitis continua of Hallopeau. Similarly, PP described in patients as old as 18 years of age appears ambiguous. 
| Conclusion|| |
The disorder appears rare largely due to unfamiliarity and infrequent reporting in the literature. We suggest that PP should be considered as a distinct entity affecting the nail unit in children ≤5 years and should be evaluated as such. Also, all those cases with identifiable etiologic factors need not be labeled as PP. Histologic features of psoriasis/pustular psoriasis (periungual skin biopsy may not always be possible in child patients) or concurrent presence of psoriasis lesions will exclude a diagnosis of PP. This will save the patient/parents from unnecessary distress and expensive therapy associated with more mutilating dermatoses of the nail unit.
| References|| |
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[Table 1], [Table 2]