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18

Rare Lung Diseases

A rare disease is defined by the U.S. National Institutes of Health Office of Rare Diseases as one that affects fewer than 200,000 people in the United States. However, there are between 5,000 and 8,000 distinct rare disorders that, together, affect more than 20 million people in the United States. A conservative estimate of primary or secondary lung involvement in 5 to 10 percent of rare diseases suggests that there are at least 1 to 2 million American patients suffering from rare lung diseases (1,2).

Whom does it affect?

Epidemiology, prevalence, economic burden, vulnerable populations As a group, uncommon lung diseases affect at least 1 in every 200 persons. Examples of rare lung diseases include sarcoidosis (see Chapter 21), an inflammatory disorder often affecting the lungs and other organs; alpha-1 antitrypsin deficiency, a genetic disorder that leads to emphysema; lymphangioleiomyomatosis (LAM), a cystic lung disease; many congenital lung disorders; a group of lung diseases affecting the blood vessels (vasculitis); rare tumors that involve the lung; rare infectious diseases such as the plague; and other disorders of

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The most "common" rare lung diseases

A

More than 1 per 100,000

B

1?10 per million

C

Dozens to hundreds of case reports

D

Isolated case reports

Infectious diseases

Fibrosing mediastinitis

Phakomatoses

Birt-Hogg-Dube

Lymphangioleiomyomatosis

Neurofibromatosis type I (with lung involvement)

Inherited forms of emphysema

Alpha-1 antitrypsin deficiency

Elastin mutations

Salla disease

Pulmonary vascular diseases

Familial pulmonary arterial hypertension

Pulmonary alveolar proteinosis

Pulmonary capillary hemangiomatosis

Pulmonary veno-occlusive disease

Hereditary hemorrhagic telangiectasia (with lung involvement)

Channelopathies

Pulmonary alveolar microlithiasis

Cystic fibrosis

Ciliary disorders

Kartagener syndrome

Primary ciliary dyskinesia

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C B B C A D D A B C C A C A B B (continued on next page)

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Rare Lung Diseases

Disorders of respiratory drive Central alveolar hypoventilation Narcolepsy

Connective tissue matrix disorders Marfan syndrome (with lung involvement) Ehler?Danlos syndrome (with lung involvement)

Genetic surfactant disorders ABCA3 SP-A-related lung disease SP-B-related lung disease SP-C-related lung disease

Trafficking and lysosomal storage disorders Hermansky?Pudlak syndrome Gaucher disease (with lung involvement) Neiman Pick C (with lung involvement)

Vasculitis Wegener's granulomatosis Goodpasture syndrome Microscopic polyangiitis (with lung involvement) Polyarteritis nodosa (with lung involvement) Churg?Strauss syndrome

Congenital Cystic adenomatoid malformation Pulmonary sequestration Neuroendocrine cell hyperplasia

Neuromuscular disease Amyotrophic lateral sclerosis

C A

C C

C D C C

B C C

A B B B A

C C B

A (continued on next page)

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Chapter 18

Myasthenia gravis

A

Dermatomyositis, polymyositis

A

Other

Sarcoidosis

A

Langerhans cell histiocytosis

B

Idiopathic pulmonary hemosiderosis

C

Sickle cell anemia (with lung involvement)

A

Lymphangiomatosis

C

Data from the Office of Rare Diseases and Orphanet (1,2).

which the cause and cellular defect may be known or unknown. Diseases of unknown etiology are termed idiopathic.

The prevalence of rare lung disorders varies widely by disease type. The lungs may also be involved as a rare manifestation of another more common disorder, such as Marfan syndrome. Some lung diseases are so rare that they only have been described in case reports. The most "common" rare lung diseases, as defined by the Office of Rare Diseases and Orphanet, occur in up to 70 patients per 100,000 (1,2).

Estimating the economic burden of rare lung disease is difficult. As a group comprising 1 to 2 million affected persons, and with a conservative estimate of average yearly healthcare expenditures of $5,000 per patient, the annual total cost is in the billions of dollars. The rarer the disorder, the more tests and healthcare

Ashley Appell, who is 23 years old, has Hermansky? Pudlak syndrome, a rare genetic disease associated with albinism, a bleeding disorder caused by abnormal platelets, and interstitial lung disease.

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Rare Lung Diseases

visits are likely required to arrive at the correct diagnosis. These delays result in greater expenses, unnecessary tests, and missed opportunities for early intervention. For example, the average interval from onset of symptoms to the diagnosis of LAM, which affects smooth muscle tissue in the lungs and airways, is three to five years (3). Most patients suffer two episodes of pneumothorax (collapsed lung) before the diagnosis is made. Misdiagnosis as primary spontaneous pneumothorax, asthma, or chronic obstructive lung disease (COPD) leads to inappropriate care and increased risk (for instance, uninformed decisions regarding pregnancy and air travel). Rare diseases are in many cases serious, chronic, and debilitating, and, once properly diagnosed, often require expensive, long-term treatments.

Rare lung diseases generally affect individuals from birth through about age 60, and are uncommon in the elderly. Some diseases are more prevalent in certain racial and ethnic populations, such as sarcoidosis in African Americans, for unknown reasons. For rare genetic lung diseases, there may be great regional variation, such as cystic fibrosis (1 in 350,000 in Japan vs. 1 in 10,000 in the United States), Hermansky?Pudlak syndrome, a disease associated with albinism, bleeding, and lung scarring (1 in 1,800 in Puerto Rico vs. only isolated case reports and small clusters in the rest of the world), and pulmonary alveolar microlithiasis, a disease associated with sand-like particles in the lung, which occurs predominantly in Japan and Turkey (4).

What we are learning about rare lung diseases?

Pathophysiology, causes: genetic, environment, microbes

The causes and pathophysiology of these diseases are varied and complex. Many have a genetic basis, and most diseases have genetic influence. The environment and micro organisms may play a role, especially in those diseases in which the patient's immune defense has been compromised. Further description of individual diseases and how they have helped researchers learn about other diseases is discussed in the last section of this chapter.

How are they prevented, treated, and managed?

Prevention, treatment, staying healthy, prognosis

Given the number and diversity of rare diseases of the lungs and other organs, it is not feasible for primary care physicians to become informed about all of

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