Unilateral Diffuse Alveolar Hemorrhage as an Initial Presentation of Microscopic Polyangiitis.

Diffuse alveolar hemorrhage (DAH) is a life-threatening condition due to widespread damage to small pulmonary vessels commonly caused by systemic vasculitis. Alveolar involvement is typically multi-lobar and bilateral. It frequently presents as bilateral diffuse airspace opacities on chest imaging. Unilateral DAH is rare. Patients presenting with hemoptysis, anemia, hypoxemia, progressive dyspnea, and opacities on chest imaging should be evaluated for systemic vasculitis such as antineutrophilic cytoplasmic antibody (ANCA) vasculitis. We report the case of a 23-year-old female who presented with hemoptysis, severe dyspnea, hypoxemia, anemia, and oliguria. The laboratory exam results showed the patient to be p-ANCA positive, which suggests a diagnosis of microscopic polyangiitis. Chest X-ray showed unilateral airspace opacities, and DAH was confirmed by hemosiderin-laden macrophages on bronchoalveolar fluid histopathological examination. After treatment with plasmapheresis, intravenous methylprednisolone pulse, and cyclophosphamide, the patient's symptoms and radiographic findings improved.

A brainstem peptide system activated at birth protects postnatal breathing.

Among numerous challenges encountered at the beginning of extrauterine life, the most celebrated is the first breath that initiates a life-sustaining motor activity1. The neural systems that regulate breathing are fragile early in development, and it is not clear how they adjust to support breathing at birth. Here we identify a neuropeptide system that becomes activated immediately after birth and supports breathing. Mice that lack PACAP selectively in neurons of the retrotrapezoid nucleus (RTN) displayed increased apnoeas and blunted CO2-stimulated breathing; re-expression of PACAP in RTN neurons corrected these breathing deficits. Deletion of the PACAP receptor PAC1 from the pre-Bötzinger complex-an RTN target region responsible for generating the respiratory rhythm-phenocopied the breathing deficits observed after RTN deletion of PACAP, and suppressed PACAP-evoked respiratory stimulation in the pre-Bötzinger complex. Notably, a postnatal burst of PACAP expression occurred in RTN neurons precisely at the time of birth, coinciding with exposure to the external environment. Neonatal mice with deletion of PACAP in RTN neurons displayed increased apnoeas that were further exacerbated by changes in ambient temperature. Our findings demonstrate that well-timed PACAP expression by RTN neurons provides an important supplementary respiratory drive immediately after birth and reveal key molecular components of a peptidergic neural circuit that supports breathing at a particularly vulnerable period in life.