Laboratory Studies
Given the myriad different ways eosinophilia-myalgia syndrome (EMS) can present, the initial workup should be directed at identifying other possible causes. Lab tests should including a complete blood count, electrolytes, kidney function, liver function, and inflammatory markers. Other studies (eg, antinuclear antibody [ANA], anti-neutrophil cytoplasmic antibodies [ANCA] should be ordered based on the clinical presentation.
Findings may include the following [8] :
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Leukocytosis can be mild to severe
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Peripheral eosinophil count greater than 1000/µL, oftentimes much higher
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Abnormal liver function study (LFT) results are common, and mild-to-moderate elevation of transaminase levels is observed in approximately 40% of patients.
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An elevated serum creatinine kinase level is uncommon, affecting only approximately 10% of patients with EMS.Elevated aldolase levels are common and occur in approximately half of patients.
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Mild-to-moderate elevation of the erythrocyte sedimentation rate (ESR) is observed in one third of patients.
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Antinuclear antibodies with a speckled pattern in low titer are observed in approximately half of patients. The significance of this is uncertain.
Imaging Studies
Imaging plays no role in the diagnosis of EMS, but patients may receive chest and/or brain imaging depending on their symptoms. Findings on such imaging may include [20] :
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Chest radiography results vary from normal to pleural effusion and/or infiltrates.Abnormalities are seen in less than one third of patients.
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Magnetic resonance imaging (MRI) of the brain has shown subcortical infarcts, focal lesions in the deep white matter, cortical atrophy, ventricular dilatation, and both diffuse and periventricular white matter abnormalities.The significance of these imaging findings is not clear.
Other Tests
Other tests such as pulmonary function tests (PFTs), echocardiography, and electrophysiologic studies may be performed based on the patient’s symptoms. Again, none of these are diagnostic of EMS. Findings include the following [8] :
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PFTs reveal a slightly decreased diffusion capacity in up to half of patients with EMS but no evidence of restrictive or obstructive lung disease.
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Electrophysiologic studies demonstrate myopathic and neuropathic changes of varying degrees. Nerve conduction studies show mixed demyelination and a pattern of axonal degeneration.
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Echocardiography typically shows normal left ventricular function and normal estimated pulmonary artery pressure, but pulmonary arterial hypertension is occasionally detected.
Procedures
Because of the varying skin rashes and muscle symptoms EMS can cause, biopsy of skin, muscle, or full thickness (epidermis to muscle) biopsy may be required to rule out other diagnoses. [8]
Histologic Findings
No consistent findings are observed in biopsy specimens from patients with EMS; therefore, histopathologic findings are helpful but not diagnostic.
Muscle biopsy commonly reveals inflammatory infiltrates, frequently perivascular, in the endomysium and perimysium. The inflammatory cells are predominantly lymphocytes and acid phosphatase–reactive histiocytes, with rare eosinophils. In some instances, microangiopathy is present. Generalized type II myofiber atrophy and denervation atrophy are common, but myofiber necrosis and degeneration are infrequent.
Skin/fascia biopsy findings generally reveal a normal epidermis. The dermis may be normal or may have perivascular infiltrates of monocytes, eosinophils, and lymphocytes without fibrinoid necrosis. These findings differ from those in patients with scleroderma, who have more collagen deposition in the dermis.
Nerve biopsy of affected nerves shows a combination of demyelination and axonal degeneration, with epineural, perineural, and perivascular cellular infiltrates. [21, 8]
