It is most pronounced when the diver is in the vertical position; the spinning is toward the ear with the higher pressure and tends to develop when the pressures differ by 60 cm of water or more. Decompression sickness
Vertigo is recorded as a symptom of decompression sickness in 5.3% of cases by the U.S. Navy as reported by Powell, 2008 including isobaric decompression sickness. Decompression sickness can also be caused at a constant ambient pressure when switching between gas mixtures containing different proportions of different inert gases. This is known as isobaric counterdiffusion, and presents a problem for very deep dives. For example, after using a very helium-rich trimix at the deepest part of the dive, a diver will switch to mixtures containing progressively less helium and more oxygen and nitrogen during the ascent. Nitrogen diffuses into tissues 2.65 times slower than helium, but is about 4.5 times more soluble. Switching between gas mixtures that have very different fractions of nitrogen and helium can result in "fast" tissues (those tissues that have a good blood supply) increasing their total inert gas loading. This is often found to provoke inner ear decompression sickness, as the ear seems particularly sensitive to this effect. Stroke
A stroke (either ischemic or hemorrhagic) involving the posterior fossa is a cause of central vertigo. Risk factors for a stroke as a cause of vertigo include increasing age and known vascular risk factors.
Other problems that can contribute to anal itching include pinworms, hemorrhoids, tears of the anal skin near the mucocutaneous junction (fissures), and skin tags (abnormal local growth of anal skin). Aside from diseases relative to the condition, a common view suggests that the initial cause of the itch may have passed, and that the illness is in fact prolonged by what is known as an itch-scratch-itch cycle. It states that scratching the itch encourages the release of inflammatory chemicals, which worsen redness, intensifies itchiness and increases the area covered by dry skin, thereby causing a snowball effect. Some authorities describe “psychogenic pruritus” or "functional itch disorder", where psychological factors may contribute to awareness of itching. Ingestion of pinworm eggs leads to enterobiasis, indicative of severe itching around the anus from migration of gravid females from the bowel. Severe cases of enterobiasis result in hemorrhage and eczema. Diagnosis
Diagnosis is usually done with a careful examination of the anus and the patients history. If the presentation or physical findings are atypical, biopsies can be done.In case of long-lasting symptoms, above all in patients over 50 years of age, a colonoscopy is useful to rule out a colonic polyp or tumor, that can show pruritus ani as first symptom. Treatment
The goal of treatment is asymptomatic, intact, dry, clean perianal skin with reversal of morphological changes. For pruritus ani of unknown cause (idiopathic pruritus ani) treatment typically begins with measures to reduce irritation and trauma to the perianal area. Stool softeners can help prevent constipation.