Varicella pneumonia, caused by the varicella-zoster virus, is a rare form of viral pneumonia. Immunocompromised individuals and pregnant women are at a higher risk of acquiring this condition, although it has been reported in immunocompetent persons too. The diagnosis of the disease is based on history, physical exam, radiological studies, and identification of viral DNA.
Varicella-zoster virus (VZV) causes chickenpox, the infectious disease which usually has a self-limiting course, especially in children. Varicella pneumonia is a complication of chickenpox seen more frequently in immunocompromised adults and pregnant women and is associated with a significant rate of morbidity and mortality . The frequency of varicella pneumonia has been reported to be 1 case in 400 patients with chickenpox infection, although it is difficult to provide an exact incidence since most published reports are about a small series of patients  .
The clinical manifestations of varicella pneumonia can range from mild to severe and their onset is up to six days after the appearance of the chickenpox rash. While some patients can be asymptomatic, the majority of patients present with clinical manifestations such as fever, malaise, dyspnea, tachypnea, dry cough, and occasionally with pleuritic chest pain, hemoptysis, and cyanosis. One study amongst military personnel showed that 25% of patients presented with a cough while 10% had tachypnea . Patients presenting with hypoxemia and severe respiratory distress usually require mechanical ventilation . Pleural effusion and peripheral lymphadenopathy are other manifestations in these cases. Some patients may rapidly deteriorate and the reported mortality rate in varicella pneumonia is 10-33% and can be as high as 50% in patients which require mechanical ventilation  .
Several risk factors have been suggested for the development of varicella pneumonia: immunocompromised status, chronic pulmonary diseases, smoking  , positive history of a contact with a patient suffering from chickenpox, being in the third trimester of pregnancy , and increased severity of the rash.
The workup includes a detailed history, clinical examination, radiological studies, and confirmation with molecular biological tests. A history of contact with an index case is a clue to the diagnosis. Physical examination will reveal the characteristic rash in various stages. In addition, occasional pulmonary wheezes and rhonchi may be found on pulmonary auscultation. Laboratory studies may show elevated lactate dehydrogenase levels (LDH) . Confirmation of hypoxemia requires pulse oximetry in all patients and arterial blood gases analysis in patients with severe disease .
Findings on plain chest X-ray frequently include round, 5-10 mm in size, confluent nodules that resolve within seven days after resolution of the cutaneous changes. However, they may persist and calcify over months, appearing as well-defined calcifications which are 2-3 mm in size. Pleural effusion may be present in some patients. Computed tomography (CT) scan shows diffusely scattered pulmonary nodules with a surrounding "ground-glass" halo.
A sample of respiratory secretions, cerebrospinal fluid (CSF), and vesicular secretions can be used to isolate the varicella-zoster virus. Multinucleated giant cells with eosinophilic intranuclear inclusions can be seen on Tzanck smear but are not specific for a varicella-zoster virus as they are also seen with a herpes simplex virus.
Direct immunofluorescence of scrapings obtained from cutaneous lesions will help to rapidly identify the varicella-zoster virus. Results of viral culture can take a long time and are not practical. Gene fragments amplification with polymerase chain reaction (PCR) and reverse-transcriptase polymerase chain reaction (RT-PCR) are the most sensitive methods to detect the varicella-zoster virus.
Rarely, a transbronchial pulmonary biopsy may be required in seriously ill, immunocompromised patients, to confirm the etiology. Histopathological examination of the lung tissue is likely to show consolidation, intranuclear inclusions, focal necrosis, and a mononuclear infiltrate.