Persistent pigmented purpuric dermatitis: granulomatous variant.

The persistent pigmented purpuric dermatitides (PPPD) are a spectrum of dermatologic disorders characterized by petechial and pigmented macules usually confined to the lower limbs. Their etiology is unknown and several clinical variants are recognized. At the microscopic level they are characterized by angiocentric lymphocytic inflammation, red blood cell extravasation and hemosiderin deposition. A granulomatous variant of the PPPD has recently been described and to date eleven cases have been reported in the literature. In contrast to the conventional type, this variant is characterized histopathologically by ill-defined, non-necrotizing granulomata admixed with the lymphocytic inflammatory background. Although initially the granulomatous variant of the PPPD was thought to occur only in Asian patients, this sole racial predilection has not been substantiated. A tenuous association with hyperlipidemia has been noted but this requires further study. The principal importance of recognizing this entity lies in the need to include it in the histopathological differential diagnosis of granulomatous dermal infiltrates. We report here an additional patient with the granulomatous variant of PPPD and elaborate on this entity in the context of existing information in the literature.

A transition probability model for amino acid substitutions from blocks.

Substitution matrices have been useful for sequence alignment and protein sequence comparisons. The BLOSUM series of matrices, which had been derived from a database of alignments of protein blocks, improved the accuracy of alignments previously obtained from the PAM-type matrices estimated from only closely related sequences. Although BLOSUM matrices are scoring matrices now widely used for protein sequence alignments, they do not describe an evolutionary model. BLOSUM matrices do not permit the estimation of the actual number of amino acid substitutions between sequences by correcting for multiple hits. The method presented here uses the Blocks database of protein alignments, along with the additivity of evolutionary distances, to approximate the amino acid substitution probabilities as a function of actual evolutionary distance. The PMB (Probability Matrix from Blocks) defines a new evolutionary model for protein evolution that can be used for evolutionary analyses of protein sequences. Our model is directly derived from, and thus compatible with, the BLOSUM matrices. The model has the additional advantage of being easily implemented.