Pathophysiology
The symptoms of CAP are the result of lung infection by microorganisms and the response of the immune system to the infection. Mechanisms of infection are different for viruses and other microorganisms. Viruses
Up to 20 percent of CAP cases can be attributed to viruses. The most common viral causes are influenza, parainfluenza, human respiratory syncytial virus, human metapneumovirus and adenovirus. Less common viruses which may cause serious illness include chickenpox, SARS, avian flu and hantavirus.Typically, a virus enters the lungs through the inhalation of water droplets and invades the cells lining the airways and the alveoli. This leads to cell death; the cells are killed by the virus or they self-destruct. Further lung damage occurs when the immune system responds to the infection. White blood cells, particularly lymphocytes, activate chemicals known as cytokines which cause fluid to leak into the alveoli. The combination of cell destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream. In addition to their effects on the lungs, many viruses affect other organs. Viral infections weaken the immune system, making the body more susceptible to bacterial infection, including bacterial pneumonia. Bacteria and fungi
Although most cases of bacterial pneumonia are caused by Streptococcus pneumoniae, infections by atypical bacteria such as Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila can also cause CAP. Enteric gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae, are a group of bacteria that typically live in the large intestine; contamination of food and water by these bacteria can result in outbreaks of pneumonia.
Periodic paralysis is a group of rare genetic diseases that lead to weakness or paralysis from common triggers such as cold, heat, high carbohydrate meals, not eating, stress or excitement and physical activity of any kind. The underlying mechanism of these diseases are malfunctions in the ion channels in skeletal muscle cell membranes that allow electrically charged ions to leak in or out of the muscle cell, causing the cell to depolarize and become unable to move.The symptoms of periodic paralysis can also be caused by hyperthyroidism, and are then labeled thyrotoxic periodic paralysis; however, if this is the underlying condition there are likely to be other characteristic manifestations, enabling a correct diagnosis. Types
Periodic paralysis is an autosomal dominant myopathy with considerable variation in penetrance, leading to a spectrum of familial phenotypes (only one parent needs to carry the gene mutation to affect the children, but not all family members who share the gene are affected to the same degree). Specific diseases include:
Hypokalemic periodic paralysis (Online Mendelian Inheritance in Man (OMIM): 170400), where potassium leaks into the muscle cells from the bloodstream. Hyperkalemic periodic paralysis (Online Mendelian Inheritance in Man (OMIM): 170500), where potassium leaks out of the cells into the bloodstream. Paramyotonia congenita (Online Mendelian Inheritance in Man (OMIM): 168300), a form which often accompanies hyperkalemic periodic paralysis, but may present alone. The primary symptom of paramyotonia congenita is muscle contracture which develops during exercise or activity. Paramyotonia congenita attacks may also be triggered by a low level of potassium in the bloodstream.