Schnitzler syndrome confused with Sweet’s syndrome

Schnitzler’s syndrome with prominent neutrophil infiltration misdiagnosed as Sweet’s syndrome: a typical example of urticarial neutrophilic dermatosis.

Asahina A, Sakurai N, Suzuki Y, Narushima K

Clin Exp Dermatol 2009 Nov 19

The authors present possible pathophysiological links and discuss new therapeutic options like tocilizumab.

Schnitzler’s syndrome is a rare disorder of unknown aetiology characterized by a chronic urticarial eruption, intermittent fever and monoclonal gammopathy. The authors came across an interesting Japanese 49 year old patient with this syndrome, who had been misdiagnosed for 10 years as having Sweet’s syndrome because of the histopathological picture, which was a prominent perivascular and interstitial neutrophilic infiltrate in the dermis with leucocytoclasia but without vasculitis. An urticarial eruption with this histopathological feature has recently been categorized as neutrophilic urticarial dermatosis, and it is strongly indicative of an associated systemic disease, mainly Schnitzler’s syndrome and other inflammatory diseases.

Clinically both conditions may be difficult to dedifferentiate as in both conditions, patients present with fever, leukocytosis (due to neutrophilia), an increase in erythrocyte sedimentation rate (ESR)[and C-reactive protein (CRP)], arthralgia and an erythematous rash. Morphologically though, this rash is an urticaria in Schnitzler’s syndrome, and “mountanous” papules of the face, neck and the extensor side of the extremities in Sweet’s syndrome.

Although Sweet’s syndrome shows a characteristic papillary derma oedema, histology is also often difficult to distinguish between the two conditions: both diseases exhibit a neutrophilic infiltrate of the dermis and sometimes spongiosis. An edema of the papillary dermis is characteristic of Sweet’s syndrome. Histology of Schnitzler’s syndrome is more variable and shows variations between neutrophilic urticaria, leukocytoclastic vasculitis and later lymphocytic urticaria

Schnitzler’s syndrome is linked to a monoclonal gammopathy (usually IgM) whereas Sweet’s syndrome is associated with a non-solid malignancy such as acute myelogenous leukaemia and multiple myeloma.

The authors have also found an increase in blood interleukin (IL)-6 levels only. This cytokine could be involved in some of the disease pathogenetical mechanisms, such as neutrophil infiltration.