Subcorneal pustular dermatosis is a rare and self-limiting, but recurring disorder of the skin distinguished by the appearance of sterile pustules in a symmetrical fashion over the trunk and the flexor parts of the extremities. The pathogenesis of this condition is incompletely understood, but it is assumed that some form of immune-mediated reaction leads to accumulation of neutrophils below the stratum corneum, which is the main feature under microscopy. Clinical findings and a biopsy of the lesion are two main components of the diagnostic workup.
Subcorneal pustular dermatosis, initially known as Sneddon-Wilkinson disease, is considered to be a rare cutaneous disorder that belongs to a group of neutrophilic dermatoses   . Although the exact etiology remains to be elucidated, skin lesions arise due to an abundant presence of neutrophils below the stratum corneum, presumably as a result of the activity of pro-inflammatory cytokines such as interleukin-8 that act as chemoattractants for neutrophils  . For some reason, subcorneal pustular dermatosis is most commonly diagnosed in middle-aged and older women aged 40 or more years  . The clinical presentation is characterized by the appearance of sterile pustular lesions on the trunk, the intertriginous areas (the axillae, the submammary areas, and the groins), and the flexor areas of the upper or lower limbs      . These pustules are symmetrically distributed and often form blistering lesions   . Despite the benign and self-limiting nature of the condition, a chronic course with frequent recurrences are hallmarks of subcorneal pustular dermatosis, which may be debilitating for the patient  . Because of the undisclosed cause, the precipitating factors for recurrence are yet to be revealed.
The differential diagnosis of subcorneal pustular dermatosis is broad, encompassing other neutrophilic dermatoses (Sweet's syndrome, acute generalized exanthematous pustulosis, and generalized pustular psoriasis) and systemic conditions that include this cutaneous disorder in the presentation, such as various lymphoproliferative disorders (eg. multiple myeloma) and immunoglobinopathies   . For this reason, the identification of subcorneal pustular dermatosis mandates a thorough workup and a histopathological examination. As a first step, however, the physician must obtain a detailed patient history that will identify the chronic and relapsing pattern of the lesions, whereas a physical exam is crucial for observing the pattern of distribution and the appearance of skin lesions. As soon as clinical suspicion is raised, a biopsy sample should be obtained for the purposes of performing a histopathological examination. The hallmark of neutrophilic dermatoses is the presence of a break below the stratum corneum that contains a dense neutrophilic infiltrate with a normal underlying epidermis    . Additionally, exclusion of immunoglobinopathies and autoimmune disorders can be made by carrying out an immunofluorescence exam that is virtually always negative  , although rare cases of immunoglobulin (Ig)A-presenting antibodies in the epidermis were documented, thus pointing toward IgA pemphigus as a potential differential diagnosis .