Why so low? An unusual case of myositis in a child

A six-year old female presented to the emergency department with a one month history of progressive right eye swelling. At this time, laboratory findings included ESR 120 mm/hr, CRP 7.2 mg/dL, HGB 10.1 g/dL, PLT 504 × 10⁹/L, normal WBC and differential, negative angiotensin converting enzyme, negative anti-serine-protease 3 antibody, and negative anti-myeloperoxidase antibody (Table 1). Brain MRI demonstrated a T2 hyperintense, well-marginated extraconal mass centered in the right superior rectus muscle. Subsequent periorbital biopsy findings were described as consistent with eosinophilic angiocentric fibrosis. She had no notable sinusitis on imaging nor cardiorespiratory symptoms. Ophthalmologic exam showed no intraorbital inflammation. She improved with 1 mg/kg of prednisone twice daily and was successfully weaned off by one year later with mild residual upper eyelid swelling and ptosis.

Six years later (age 12), she presented to pediatric rheumatology clinic with a two month history of bilateral calf pain and tightness with difficulty ambulating. She had a normal review of systems including no fever, fatigue, night sweats, or recent travel. Recent ophthalmologic follow-up exam showed no inflammation. She did not take medications and had an unremarkable family history. Exam revealed tender, swollen calves with limited ankle range of motion and strength due to pain and tightness. She had an antalgic gait. She had no hepatosplenomegaly, arthritis, rash, or abnormal cardiopulmonary findings on exam. Labs at this visit demonstrated ESR 112 mm/hr, CRP 7 mg/dL, HGB 9.1 g/dL, and MCV 65.6 with normal muscle markers and mildly elevated complement (Table 1). She had an IgG of 4040 mg/dL (503–1719), determined to be a polyclonal hypergammaglobulinemia. She also had a normal or negative ANA profile, anti-serine protease 3 antibody, anti-myeloperoxidase antibody, angiotensin converting enzyme, lysozyme, serum calcium, creatinine, aldolase, uric acid, T4, and TSH. MRI of the distal lower extremities demonstrated extensive bilateral myositis of the lower legs with both active inflammation and atrophy and to a lesser extent fasciitis (Fig. 1A). During this period of diagnostic assessment, the patient’s leg pains self-resolved and the patient was lost to follow-up.

The patient presented again to rheumatology three years later, at age 15, with three weeks of lower leg pain with swelling and tightness and an otherwise unremarkable history and exam. Her labs revealed ESR 107 mm/hr, CRP 7.5 mg/dL, and IgG 3240 mg/dL with a normal SPEP (predominantly IgG1). She tested positive for lupus anticoagulant (dilute Russell viper venom test) and anti-beta-2 glycoprotein-1 IgM and had an elevated d-Dimer, PTT, and PT. ANA profile and muscle enzyme levels remained negative (Table 1). Chest radiograph was normal. MRI with and without contrast revealed normal pelvis and thigh musculature but diffuse muscular edema consistent with severe myositis throughout her lower legs with associated fatty infiltration indicative of muscular atrophy (Fig. 1B).

A biopsy of her left gastrocnemius muscle was performed, demonstrating non-caseating granulomatous myositis with perivascular inflammation, extensive muscle fibrosis, and fatty replacement of the muscle (Fig. 2A,B). Special stains of the granulomas demonstrated a histiocytic component with CD4 + T cell predominance consistent with sarcoidosis (Fig. 2C,D). Further pathologic assessment excluded microorganisms, inclusion body myositis, and IgG4 disease.

Re-examination of her right peri-orbital biopsy from 9 years earlier also revealed a CD4 + T cell-predominant inflammatory cell infiltrate within the skeletal muscle similar to the current findings in her gastrocnemius, although no granulomas were found. She had a normal chest x-ray and no uveitis, lymphadenopathy, arthritis, or rash.

The patient was diagnosed with sarcoid myositis and prescribed 20 mg oral prednisone daily, iron (for iron deficiency), and physical therapy.

Over the next two months, she had significant improvement in her symptoms and inflammatory markers (Table 1). She began 20 mg oral methotrexate weekly with further resolution of symptoms (apart from chronic muscle tightness) when seen 4 months later on 10 mg prednisone. A few months after that visit, she self-discontinued her medications and experienced return of symptoms and lab abnormalities after one month (Table 1). Chest radiograph remained normal. Ultrasound with venous doppler of her more tender left lower extremity was reassuring against clot. Abdominal and pelvic CT performed soon after due to a motor vehicle accident showed no intrabdominal masses or concerning pathology. She was once again lost to follow-up.

This is the second reported case of granulomatous myositis associated with sarcoidosis in a pediatric patient, and the first to present with a chief complaint of leg pain. While the histopathology results eventually confirmed the diagnosis, we first considered many other diagnoses given the unusual presentation of pain and inflammation localized to bilateral calves in a child.

The differential diagnosis for myositis in children includes rheumatic diseases (e.g. juvenile dermatomyositis/polymyositis, vasculitis, eosinophilic fasciitis, systemic lupus erythematosus, or IgG4-related disease), as well as infection, malignancy, paraneoplastic syndromes, and genetic, metabolic, neurologic, or toxic myopathies. Of all these conditions, only rare distal muscular dystrophies and inclusion body myositis are known to cause isolated lower leg myositis and inclusion body myositis is almost exclusively found in adults. When present in adults, symptomatic lower leg myositis is typically unilateral and involves the gastrocnemius, vastus lateralis, and adductor muscles [20, 21]. Systemic rheumatologic diseases such as juvenile dermatomyositis and polymyositis are often more proximal in nature, while vasculitis typically includes systemic symptoms and would be unlikely to cause regional muscle inflammation isolated to symmetric regions. Infectious myopathies are also unlikely to present in symmetric areas. Concern for IgG4-related disease was raised given her prior peri-orbital inflammation; however, staining of both biopsies excluded this. Her peri-orbital muscle inflammation and granulomatous myositis of her lower extremities also raised concern for granulomatosis with polyangiitis; however, she had no signs of vasculitis on histopathology, imaging, or exam and negative anti-neutrophil cytoplasmic antibodies [22]. Lastly, the intermittent nature of her flares over the years was unusual for any of these diagnoses - though given the degree of atrophy seen, it is likely that some inflammation persisted between presentations.

As demonstrated, a diagnosis of sarcoidosis requires consideration of a multitude of diagnoses. In these diagnostic dilemmas, a thorough laboratory evaluation must assess for signs of inflammation (CBC, ESR, CRP, IgG) and muscle injury (CK, LDH, AST, and aldolase). Unfortunately, results in this patient were non-specific and her significantly elevated IgG raised concern for monoclonal gammopathy or multiple myeloma initially, though SPEP was reassuring. While she did have a positive lupus anticoagulant, this finding has low specificity and she lacked other antiphospholipid antibodies, signs and/or symptoms of thrombosis, or markers of systemic lupus erythematosus. Ultimately, tissue biopsy was deemed necessary and led to a diagnosis of granulomatous myositis. While granulomatous myositis can be seen in the context of infections (such as tuberculosis), inflammatory bowel disease, vasculitis, malignancy, thymoma, and myasthenia gravis, [23] her presentation, negative staining for infectious pathogens, and lymphohistiocytic infiltrate with CD4 + T cell predominance confirmed the diagnosis of sarcoid myositis. With this knowledge, re-evaluation of her prior periorbital biopsy further supported a diagnosis of sarcoidosis.

There are 3 clinical patterns of sarcoid myositis reported in the literature: acute inflammatory myositis with myalgia (typically presents early on and in young patients), chronic myopathy with progressive weakness (typically presents late and is the most common pattern), and nodular myopathy with palpable muscle nodules. Our patient presented with acute inflammatory myositis with myalgia that progressed toward chronic myopathy. It is important to note that markers of sarcoidosis (angiotensin converting enzyme and lysozyme) are often negative in children. Additionally, markers of muscle inflammation may be normal in sarcoid myositis, as seen in our patient.

Interestingly, our patient had no other features of sarcoidosis, apart from elevated inflammatory markers and her histopathology, despite almost a decade of disease activity affecting various muscles. This is in contrast to the one previously reported pediatric case of sarcoid myositis in which a child presented at 16 years of age with hypercalcemia and renal insufficiency and was subsequently found to have non-caseating epithelioid granulomas and calcium oxalate crystals in her skeletal muscle after abnormalities were noted on exam and imaging [24].

Little is known about the optimal treatment of sarcoidosis in children, including sarcoid myositis. While sarcoidosis typically responds to glucocorticoids, the response of sarcoid myositis to glucocorticoids is unpredictable [7, 10, 12, 15, 25, 26]. Both our patient and the previously reported pediatric patient responded well to prednisone and methotrexate with relapse upon glucocorticoid withdrawal. The 16-year-old went into remission with the addition of adalimumab while our patient was lost to follow-up. There are reports of successful treatment of adults with sarcoid myositis with glucocorticoids [10, 27] with or without methotrexate [28] as well as other immune modulating agents, including TNF-antagonists.

In summary, sarcoid myositis is an underrecognized manifestation of sarcoidosis with very little known regarding its presentation and course in children. In this patient, sarcoid presented as bilateral lower leg myositis, a rare distribution of myositis that required a broad differential diagnosis and targeted work-up. This patient also fell into the rare subgroup of patients with symptomatic muscle involvement [12]. Further characterization of sarcoid myositis in children and its management will enhance care for children with this potentially devastating disease.