Throughout the AMA Guides there are some medical conditions that are rarely, if ever, seen in industrial injuries or accidents.  When those rarely seen medical conditions emerge within the context of an industrial injury, the question will always arise as to whether the treating or evaluating physicians properly apply the AMA Guides in assessing that condition for an impairment rating.

One of those conditions is industrially related asthma.  So far, we have seen three industrial asthma cases in which the treating physicians, AMEs and a panel QME have not correctly applied Chapter 5 of the AMA Guides in determining an accurate permanent impairment rating.  The following is a step by step analysis of what Chapter 5, The Respiratory System in the AMA Guides, require to obtain an accurate impairment rating for asthma.

ASTHMA

There is a special need to discuss asthma cases and how the authors of the AMA Guides determine impairments as a result of occupationally related asthma disease.  We have seen many asthma cases over the years and will continue to do so and the method of rating permanent disability for asthma has changed dramatically from the method utilized under the 1997 PDRS.  The 1997 PDRS based permanent disability ratings for asthma on the severity of the asthma and its effect on a person’s ability to exert him or herself for work activities.  A “limitation from exposure to dust, fumes and particulates; heavy work and emotional stress” was a common work restriction for someone with severe industrially related asthma.

Asthma is defined in Section 5.5 on page 102 of the AMA Guides as an inflammatory disease with episodic and variable airway flow limitation and airway hyper-responsiveness.  Symptoms include cough, sputum, wheeze, chest tightness or dyspnea (shortness of breath).  There also has to be evidence of:

1. Reversible airflow obstruction or airway reactivity to a methacholine challenge, or
2. Histamine challenge if there is no airflow limitation but the patient has symptoms of asthma.

An asthma attack can be induced by exposure to dust, fumes, particulates; exercise, or emotional stress.  The authors of the AMA Guides do not discuss asthma attacks caused by emotional stress and very little is mentioned about exercise induced asthma attacks.

A person’s airflow obstruction is usually caused by the inflammation of the bronchial and/or lung tissue and is measured by a standard pulmonary function test.  Airway hyper-responsiveness is tested by a methacholine or histamine challenge where the physician exposes the patient to a known irritant and tests for the level of concentration of the irritant at which the patient has a negative airway reaction and the FEV₁ decreases by at least 20%.

The authors of the AMA Guides on page 102 acknowledge the significant existence of occupational asthma:

“Besides directly causing occupational asthma, work exposures can acutely exacerbate an underlying asthmatic condition, which can subsequently return to pre-exposure baseline status with removal from exposure.  Work exposures can also cause a more permanent change in an underlying asthmatic condition, which can persist even after removal from exposure… Occupational asthma can be caused by sensitizers or irritants.”

Sensitizers are substances (like grain dust, paper dust, latex, di-isocynate, animal dander) that require a latency period for the development of an asthmatic response.  The authors of the AMA Guides also indicate that once there is an onset of symptoms, there is a potential for a severe exacerbation or fatality upon further exposure.  Over 50% of asthma sufferers who have sensitized-induced asthma do not recover completely even after two or more years since the last exposure.

Irritant-induced asthma is also known as “RADS” or “reactive airways dysfunction syndrome.”  This is the type of asthma that can occur with a single high level exposure to a highly irritating gas, fume, mist or vapor. For a diagnosis of RADS, there has to be all of the following components:

1. Inhalation exposure to an acutely irritating substance.
2. Onset of asthmatic symptoms within 24 hours of exposure to the irritant with persistent respiratory symptoms.
3. Functional abnormalities (airway hyper-responsiveness) for greater than three months without pre-existing respiratory disease.

The AMA Guides 5th edition, which was published in 2000, adopts national asthma testing standards in effect in 1993 by the ATS (American Thoracic Society).  The ATS guidelines require proper testing to correctly diagnose asthma as follows:

1. If the pre-bronchodilator FEV₁ is above the lower limit of normal for a patient who has clinical symptoms of asthma then the physician is required to perform a methacholine challenge.
2. If the pre-bronchodilator FEV₁ is below the lower limit of normal then the degree of reversibility is assessed with inhaled bronchodilator.

The reason for the distinction is because many sensitized-induced asthma patients will have below normal FEV₁ as a result of the asthmatic condition which is partially reversed with a bronchodilator while other asthma patients who have had irritant induced asthma will have significantly reduced (over 20%) FEV₁ with exposure to a very low concentration of the irritant (methacholine).

Table 5-9 utilizes a multifactoral method of assessing permanent impairment in the form of an “asthma severity score” which then is used to determine a WPI rating.  The asthma severity score is derived from a score for optimal drug treatment, plus a score for the post-bronchodilator FEV₁ and/or the score for the degree of reversibility of the FEV₁ related to the amount of irritant in a challenge necessary to reduce the FEV₁ by at least 20%.

In order to determine WPI from occupational asthma, the physician has to do the following:

1. Determine optimal medication if the Applicant is MMI.
2. Determine FEV₁ post-bronchodilator.
3. Determine reversibility of FEV₁ after a challenge.
4. Use Table 5-9 to calculate asthma severity score by adding scores for optimal medication, FEV₁ post-bronchodilator and/or FEV₁ reversibility after a challenge.
5. Use Table 5-10 to convert asthma severity score to WPI taking into account a detailed description of how the Applicant’s asthma affects his or her ADL functioning pursuant to Table 1-2 on page 4 of the AMA Guides.  First, determine which Class of permanent impairment and then state what WPI rating is within the Class.  State how and why the physician came to his or her conclusions for the asthma severity score, the WPI Class and the actual WPI within the Class.

In order to properly and completely apply Table 5-9 in an asthma case, you must make sure the physician reads and follows the instructions in the footnotes below Table 5-9.  These footnotes require the physician to add the asthma severity scores for medication use, FEV₁ post-bronchodilator and FEV₁ reversibility if there was a methacholine or histamine challenge.  The footnotes under Table 5-9 states:

“FEV₁ indicates forced expiratory volume in the first second; PC₂₀ is the provocative concentration that causes a 20% fall in FEV₁.  Add the scores  for post-bronchodilator FEV₁, reversibility of FEV₁ (or PC ₂₀) and medication use to obtain a summary severity score for rating respiratory impairment.”

There is a second footnote under Table 5-9 that explains when to use the reversibility score and when to use the provocative concentration score:

“When FEV₁ is greater than the lower limit of normal, PC ₂₀ should be determined and used for rating of impairment; when FEV₁ is less than 70% of the predicted, the degree of reversibility should be used; and when FEV₁ is between 70% of the predicted and the lower limit of normal, either reversibility or PC ₂₀ can be used.  The score for minimum medication use is added to the appropriate measurement criteria outlined above.”

Finally, another footnote refers to the minimum medication use which should be determined by the testing physician through previous records of exacerbation when medications have been reduced.  Remember, “normal limits” of FEV₁ are determined by the pulmonary function tables, Tables 5-4a – Table 5-5b on pages 97 and 98 of the AMA Guides.

Since the asthma severity scoring system reflected in Table 5-9 is based upon criteria established in 1993, it is probable that newer medications and better testing methods of FEV₁ may alter the scoring for asthma severity.  Physicians can determine the medication score by comparing new medications with the established ones listed in Table 5-9.  However, prednisone use is still the gold standard in severe cases.  The methacholine challenge is still used in 2008 in cases where a person has symptoms of asthma but whose pre-bronchodilator FEV₁ is at the lower limit of normal.

Once the physician determines the asthma severity score from Table 5-9, the score is then used to determine the WPI Class due to the asthma using Table 5-10 which is substantially as follows:

*A score of 10-11 means that there is uncontrolled asthma despite maximum treatment, a less than 50% post-bronchodilator FEV₁ despite over 20mg/day of prednisone.

The physician then establishes the WPI rating within a class by describing the effects of the asthma on the Applicant’s ADL functioning.  For example, in the school maintenance worker case in Section 8.05[1][d] on page 8-26 of The Lawyer's Guide to the AMA Guides and California Workers' Compensation, based on Table 5-9, the Applicant had post-bronchodilator FEV₁ of 69% of predicted (asthma severity score of 2), FEV₁  change (reversibility) of 10% where the bronchodilator did not work that well (asthma severity score of 1), no challenge test (due to below normal FEV₁ post-bronchodilator) (asthma severity score of 0) and minimum medication use of “bronchodilator on demand and daily high dose inhaled corticosteroid or one to three courses a year of systemic corticosteroid” (asthma severity score of 3):

Post-bronchodilator FEV₁:         Asthma severity score = 2

FEV₁ reversibility:                     Asthma severity score = 1

No methacholine challenge:       Asthma severity score = 0

Optimal medication use:            Asthma severity score = 3

                                        Total asthma severity score = 6

The footnote below Table 5-10 states: “The impairment rating is calculated as the sum of the individual’s scores from Table 5-9.”  On Table 5-10, this Applicant has a Class 3 whole person impairment based upon the total score from Table 5-9.  The AME indicated that since the Applicant was able to return to work with the use of a cartridge respirator, he was stable and compliant with his medication and his ADL functioning was fairly normal, he was assigned a 26% WPI – the lowest end of a Class 3.  The WPI rating of 26% resulted in a 58% permanent disability award.

Some people have significant side effects from asthma medications, especially with prednisone.  Corticosteriods like prednisone can cause among other things weight gain, diabetes, osteoporosis and a compromised immune system.  Any significant side effects from asthma medications should be separately assessed and rated by the physician independently from the WPI rating for the asthma alone.

As you can see, assessment of asthma to determine an impairment rating under the AMA Guides is quite a challenge for the physician and for counsel, the judge and the claims examiner.