Less than 1% of patients with adenocarcinoma of the lung will exhibit this finding, but when it does occur, it is a poor prognostic factor. The exact mechanism of HPO is unknown but it thought to be hormonal or neurogenic in etiology. The triad of HPO includes distal clubbing, arthritis, and bilateral symmetrical periosteal formation. Causes
Risk factors
According to the Nurses Health Study, the risk of pulmonary adenocarcinoma increases substantially after a long duration of tobacco smoking: smokers with a previous smoking duration of 30–40 years are more than twice as likely to develop lung adenocarcinoma compared to never-smokers (relative risk of approximately 2.4); a duration of more than 40 years increases relative risk to 5.This cancer usually is seen peripherally in the lungs, as opposed to small cell lung cancer and squamous cell lung cancer, which both tend to be more centrally located, although it may also occur as central lesions. For unknown reasons, it often arises in relation to peripheral lung scars. The current theory is that the scar probably occurred secondary to the tumor, rather than causing the tumor. The adenocarcinoma has an increased incidence in smokers, and is the most common type of lung cancer seen in non-smokers and women. Deeper inhalation of cigarette smoke results in peripheral lesions that are often the case in adenocarcinomas of the lung. Generally, adenocarcinoma grows more slowly and forms smaller masses than the other subtypes. However, it tends to metastasize at an early stage.
Progressive outer retinal necrosis (PORN) syndrome is a form of chorio-retinitis, an infection in the retina, the back of the eye. The disease is most commonly caused by the Varicella zoster virus and is found almost exclusively in patients with HIV/AIDS (acquired immunodeficiency syndrome). Progressive outer retinal necrosis is the second most common opportunistic retinal infection in North America among people with AIDS. The reason this disease process is considered opportunistic is precisely because it only presents in patients with AIDS, a disease that attacks and weakens the immune system, making space for other infections, like Varicella zoster virus (VZV) and Herpes simplex virus (HSV), to attack the body. The syndrome, PORN, falls under the umbrella of Necrotizing Herpetic Retinopathy, along with Acute Retinal Necrosis (ARN). Although fairly similar processes, the two forms of retinopathy have different presenting symptoms. Acute Retinal Necrosis, or ARN, is damage more central in the retinal portion of the eye with dead or necrotic areas well defined. ARN also presents with inflammation within the eye and is often painful. Progressive outer retinal necrosis (PORN) is a chorioretinitis presenting with multiple lesions in the peripheral retina. Unlike ARN, this disease process has no signs of intraocular inflammation, the hallmark feature, or vascular involvement. Presentation (Signs and Symptoms)
The presentation of the disease is dependent on the patients AIDS prognosis. If the immune system has been significantly weakened by AIDS, a patient will likely present with worse and faster progressing PORN.