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Hot tub lung can mimic tuberculosis, sarcoidosis.

KEYSTONE, COLO. -- Hot tub lung is a common, frequently misdiagnosed, and particularly fascinating form of nontuberculous mycobacterial pulmonary disease, according to a researcher from the National Jewish Medical and Research Center, Denver.

Hot tub lung is believed to be a hypersensitivity pneumonitis caused by exposure to aerosolized Mycobacterium avium complex (MAC) and other nontuberculous mycobacteria (NTM) predisposed to grow in indoor hot tubs, enclosed swimming pools, spas, and therapy pools.

"The thought is the lung is overre-sponding to an antigen. What we don't know is whether it's simply an immune response to an antigen or a true infection with an NTM organism," Dr. Gwen A. Huitt said at a meeting on allergy and respiratory diseases sponsored by the National Jewish Medical and Research Center.

And that unresolved question bears on the issue of optimal treatment. "We still don't have a conclusion as to what the right treatment is: strict exposure avoidance and prednisone, or antibiotics as well. I think the jury is definitely still out," said Dr. Huitt, director of the adult infectious disease care unit and chairman of the infection control committee at the center.

Indeed, Dr. Huitt noted that in a recent series of 27 patients with hot tub lung reported by her colleagues in the occupational medicine group at National Jewish, the disease resolved or improved with treatment in all cases. However, one-third of patients were left with a mild, fixed, permanent residual impairment in lung function as evidenced by a diffusing capacity of the lung for carbon monoxide less than 80% of normal. So hot tub lung isn't necessarily a benign process.

All patients were treated with exposure avoidance, 13 got oral prednisone alone tapered over 4-8 weeks, and 12 got prednisone plus 3-6 months of triple-agent antimycobacterial therapy. There was no significant difference in the residual impairment rate between patients treated with or without antimycobacterial drugs (J. Occup. Environ. Hyg. 2007;4:831-40).

Her tentative conclusion? "Prednisone may be enough as long as you're avoiding the exposure."

Patients with hot tub lung typically are previously healthy and younger than those with other NTM-associated pulmonary disease. Recreational tub and pool users aren't the only at-risk population. The disease also occurs in pool maintenance workers, lifeguards, and water therapists, raising occupational health issues.

The main presenting symptoms of hot tub lung are subacute-onset shortness of breath, cough, and fatigue. "Many of these patients feel like they have a slow-onset flu. They're achy, tired, have a prominent cough or arthralgias," according to Dr. Huitt.

Chest x-rays will show diffuse infiltrates with prominent nodularity in all lung fields. CT scans often show intense inflammation with centrilobular nodules, ground glass opacities in a mosaic pattern, and air trapping.

Diagnosis of hot tub lung is based on a history of exposure, compatible radiographic studies, and positive cultures for NTM obtained from the hot tub water as well as from sputum, bronchoaveolar lavage, or lung biopsy, Pulmonologists at National Jewish have found that lidocaine is bacteriocidal to NTM; they've learned to rely instead on conscious sedation in order to avoid false-negative cultures when performing bronchoscopy in patients with suspected NTM.

Interestingly, the referral diagnosis was hypersensitivity pneumonitis in only 8 of the 27 patients in the recent National Jewish series. One-quarter of patients had a working diagnosis of sarcoidosis, probably because lung biopsies obtained at other centers showed granulomas. But the granulomas characteristic of hot tub lung are discrete, nonnecrotizing, and distributed in a bronchocentric and centrilobular fashion, in contrast to sarcoidosis.

The remaining patients were misdiagnosed elsewhere as having asthma, pneumonia, emphysema, tuberculosis, bronchiolitis obliterans, or interstitial lung disease.

Dr. Huitt recalled a recent consult she received from public health workers regarding a family of five who'd been diagnosed with TB and quarantined while undergoing anti-TB therapy.

It was a well-to-do white family living in an affluent community, and they had no history of travel to an endemic area. Dr. Huitt grew suspicious. Do they have an indoor hot tub? she asked. Sure enough, they did. And depressed by the quarantine and TB drug side effects, they were spending a lot more time in it than usual, and--strangely enough--feeling worse and worse. They hadn't changed the water in months and months--it's quite expensive--although they regularly dumped in disinfectant chemicals. A thorough work uprevealed all five had hot tub lung rather than TB.

Dr. Huitt's preferred method of NTM exposure avoidance involves ripping out the hot tub. She stressed that while hot tub manufacturers tout their disinfectant systems, which often rely on UV light, bromine, chlorine, or ozone, none of them kills mycobacteria.

"The word needs to get out: The only thing that really works is changing the water," Dr. Huitt said. "After a nuclear bomb, there will still be cockroaches and mycobacteria."

BY BRUCE JANCIN Denver Bureau
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Title Annotation:Pulmonary Medicine
Author:Jancin, Bruce
Publication:Internal Medicine News
Article Type:Disease/Disorder overview
Geographic Code:1USA
Date:May 1, 2008
Words:796
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