They have an insidious onset of cough, progressive dyspnea, fatigue, and weight loss. This is associated with partial to complete but gradual reversibility. Avoiding any further exposure is recommended. Clubbing is observed in 50% of patients. Tachypnea, respiratory distress, and inspiratory crackles over lower lung fields often are present. In fact, hypersensitivity pneumonitis can often resemble (IPF) in terms of pulmonary fibrosis and that many patients experience hypoxemia. Epidemiology
Although the prevalence of hypersensitivity pneumonitis is not established it is thought to be low. Data collection limitations are a result of difficulty in diagnosis, sub-clinical presentations that go undetected and variability in climate, region and proximity to local industries. The most common types are bird fanciers and farmers lung. Interestingly, cigarette smoking appears to be protective against the disease. Pathophysiology
Hypersensitivity pneumonitis is caused by an exaggerated immune response (hypersensitivity). Type III hypersensitivity and type IV hypersensitivity can both occur depending on the cause. In general, acute HP is suspected to be attributed to a type III hypersensitivity while the subacute and chronic types are suspected to be caused by T cell infiltration and granuloma formation. Because different people react variably to antigen exposure, the exact mechanism is unclear but genetic and host factors are likely at play. The two hit hypothesis is often toted in the literature to explain why some people have a normal reaction to an antigenic exposure without clinical findings while others experience an exaggerated immune response.
Crotamiton is a drug that is used both as a scabicidal (for treating scabies) and as a general antipruritic (anti-itching drug). It is a prescription, lotion-based medicine that is applied to the whole body to get rid of the scabies parasite that burrows under the skin and causes itching. Use
For treating scabies, crotamiton should be applied to the whole body rather than a localized area. It is applied two or three times, with a 24-hour delay between applications, and the patient is asked to take a shower no sooner than after 48 hours. For children under 3 years, it is applied once daily. It can also be used to treat itching stemming from other causes, e.g. insect bites, in which case it is applied to the itching areas only, and repeated if necessary after 4 to 8 hours. Use near the eyes, or breaks in the skin, should be avoided. Pharmacology
Crotamiton is toxic to the scabies mite. It probably acts as a general antipruritic by inhibition of TRPV4, a sensory ion channel that is expressed in the skin and primary sensory neurons. Pharmacokinetics
After topical application, crotamiton is absorbed systemically. It has an elimination half-life of 30.9 hours and 4.8-8.8% is excreted in the urine. Side effects
The most common side effect of crotamiton is skin irritation. Trade name
Crotamiton is marketed under the trade names Eurax, which is manufactured by Ranbaxy Laboratories in the United States, and GlaxoSmithKline in the United Kingdom, and Euracin, which is manufactured by Green Cross in South Korea.