A Strong Diagnosis of Weakness

Though there is a concern for sarcoidosis, this diagnosis can only be confidently made by finding noncaseating granulomas on a background of compatible clinical and radiologic findings after alternate possible etiologies are excluded. The chest CT reveals a small ground-glass density lesion without hilar adenopathy. These findings, though not incompatible, are not typical for pulmonary sarcoidosis. Therefore, finding noncaeseating granulomas in a second organ system would point toward systemic sarcoidosis as a unifying diagnosis. Bronchoscopy with bronchoalveolar lavage (BAL) and transbronchial biopsy has a reasonable yield even in the absence of hilar adenopathy or typical parenchymal findings. A CD4/CD8 T-cell ratio of 2 or more on BAL provides supportive evidence for sarcoidosis.

It is reasonable to start empiric glucocorticoids for GM given that the AFB and fungal stains on histopathology are negative and that there is no evidence of lymphoma.

The CD4/CD8 T-cell ratio greater than 2, combined with the absence of neutrophils and eosinophils on BAL, is helpful in distinguishing sarcoidosis from other pulmonary diseases. This patient’s inflammatory myopathy was revealed to be a rare initial manifestation of systemic sarcoidosis.

Weakness is a common symptom of muscle disorders such as myopathies and muscular dystrophy. Idiopathic inflammatory myopathies include PM, DM, and others.^1,2 These usually present with proximal-dominant muscle weakness, decreased endurance, and muscle inflammation. A diagnosis is made according to symptoms in combination with diagnostic examinations, including elevated serum CK levels, abnormal EMG findings, and histopathology of skeletal muscle biopsy specimens.

Sarcoidosis, a multisystem disorder of unknown etiology, is characterized histopathologically by noncaseating granulomas in affected organs.³ It typically affects young adults, with incidence peaking at 20 to 39 years of age. Although any organ may be involved, the disorder usually presents with 1 or more common abnormalities, including bilateral hilar lymphadenopathy, lung lesions, and skin and eye involvement. Musculoskeletal involvement is less common. It is estimated that skeletal muscle is involved in 50% to 80% of patients with sarcoidosis but is rarely symptomatic (0.5% to 2.5%).^4-6

In this patient, weakness was distributed in both proximal and distal muscles, yet proximal weakness is the most characteristic feature in PM and DM. Therefore, sarcoidosis should be considered in the differential diagnosis of idiopathic inflammatory myopathies, especially when weakness accompanies abnormalities in other organs typically affected by sarcoidosis.

Myoglobinuria often is observed in rhabdomyolysis and inflammatory myopathies, conditions that produce high levels of serum CK and myoglobin. Myoglobinuria, often accompanied by the elevation of urinary β2-microglobulin and N-acetyl-D-glucosamine levels, can induce tubulointerstitial damage, which leads to acute kidney injury. In this case, however, these abnormal kidney findings were observed without high levels of serum CK or myoglobin. This suggests the potential for other causes of tubulointerstitial damage, such as granulomatous interstitial nephritis in renal sarcoidosis.³

Another characteristic abnormality was the elevation of urinary calcium excretion, which indicated an underlying granulomatous disorder, such as mycobacterial infection, granulomatosis with polyangiitis, or sarcoidosis. In sarcoidosis, hypercalciuria occurs in 40% of patients, hypercalcemia in 11%, and renal calculi in 10%.^3,7 Hypercalciuria, for this patient, was important in arriving at the correct diagnosis after the gallium scan was obtained given the dearth of other typical features of sarcoidosis.

Although muscle biopsy is essential, imaging studies for idiopathic inflammatory myopathy are considered useful tools to narrow the differential diagnosis. The use of MRI of the skeletal muscle is helpful to both identify an adequate muscle for biopsy and demonstrate the pattern of affected muscles beyond clinical appearance, which aids in excluding, for example, muscular dystrophies.^8,9

FDG PET/CT is a very sensitive imaging modality used to detect neoplastic lesions and has been widely used to screen for occult neoplasms and detect metastases.^10-12 It is also useful for detecting inflammation in patients with osteomyelitis, metastatic infectious diseases, rheumatoid arthritis, vasculitis, inflammatory bowel diseases, fever of unknown origin, and sarcoidosis.^11,12 In PM and DM, however, the sensitivity of FDG PET/CT for detection of myositis is reportedly lower than that of EMG and MRI.¹³ Similarly, gallium scintigraphy is usually performed to examine the disease activity of interstitial pneumonia or to detect malignancy. Previous literature and this case show that the striking images of gallium scintigraphy and FDG PET/CT have utility, not only for detection of sarcoid myopathy but also for the evaluation of treatment efficacy.^14-17 Characteristic imaging findings on FDG PET/CT have been described as a “tiger man” appearance.¹⁷

For the treatment of sarcoid myopathy, systemic glucocorticoids are used for patients with symptomatic acute or chronic forms. The standard doses of prednisolone used for other forms of idiopathic inflammatory myopathies are usually administered.^3-6 In general, the response of acute sarcoid myopathy to glucocorticoid therapy is favorable, and the clinical course is usually benign. However, the course in chronic sarcoid myopathy can be unpredictable with exacerbations. Given the lack of randomized trials of this therapy and because glucocorticoids themselves can cause steroid-induced myopathy, they are not used for asymptomatic patients.

In the end, astute clinical thinking, deductive reasoning, and pattern recognition were all instrumental in making this strong diagnosis of weakness.