Histopathology could help distinguish monomorphic maculopapular cutaneous mastocytosis (mMPCM) from other subtypes of pediatric mastocytosis, according to researchers from the Netherlands.

“The presence of clear MC [mast cell] infiltration of the papillary dermis could be used to exclude mMPCM when the clinical phenotype is not entirely clear,” the researchers said. Papillary sparing by infiltration showed a sensitivity of 88.9% and a specificity of 62.5% to detect mMPCM. Positive and negative predictive values were 72.7% and 83.3%, respectively.

The analysis of skin biopsies revealed that mMPCM patients were almost devoid of mast cell infiltration in the papillary dermis, whereas patients with polymorphic MPCM (pMPCM) or diffuse cutaneous mastocytosis presented with high numbers of mast cells in the papillary dermis. On the other hand, the number of mast cells in the reticular dermis was similar between mMPCM and pMPCM.

The researchers found increased number of mast cells in all patients, particularly in those with diffuse cutaneous mastocytosis. Patients with mMPCM and polymorphic MPCM (pMPCM) showed comparable levels. Patient age at the time of skin biopsy was negatively correlated with the number of mast cells in skin. Pediatric mMPCM patients had a higher mean mast cell count in total skin and in each skin layer than adult mMPCM patients.

Read more about SM

Furthermore, basal pigmentation and vascular ectasia were more frequently observed in mMPCM patients compared to other mastocytosis subtypes, and spindle-shaped mast cells were observed in all adults, but only in 50% of children with mMPCM and in 25% of children with pMPCM.

The expression of aberrant markers, including CD2, CD25, or CD30, was similar in all pediatric groups and was minimal or absent in adult patients.

Read more about SM epidemiology

The study enrolled 33 patients (age range, 0-69 years), with most having childhood onset of mastocytosis (n=26). Pediatric diagnoses included mMPCM (n=10), pMPCM (n=8), mastocytoma (n=5), and diffuse cutaneous mastocytosis (n=3). Five children with mMPCM had SM. All adult patients had adult-onset mMPCM and 5 had indolent SM.

Reference

Hermans MAW, Pasmans SGMA, Arends NJT, et al. Histopathological characteristics are instrumental to distinguish monomorphic from polymorphic maculopapular cutaneous mastocytosis in children. Clin Exp Dermatol. 2022;47(9):1694-1702. doi:10.1111/ced.15262