Sickle Cell Disease with Dermatomyositis - a Rare and Complex Comorbidity

Introduction and Case Presentation - A 4 yrs old female with sickle cell disease (SCD) and intermittent asthma presented with polyarthralgia predominantly involving bilateral hip and knee joints and became non-ambulatory over a course of 2 months. She developed chronic facial swelling, and a pruritic erythematous rash involving face, extensor surface of the hand and the right knee with significant weight loss. Physical examination was significant for heliotropic rash on the eyelids, Also present were Gottron's papules and macules on both hands and right knee along with right leg tenderness, muscle weakness, wasting and decreased range of motion at bilateral hip joints along with inguinal lymphadenopathy. Investigations were significant for severe anemia with hyperactive bone marrow, metabolic acidosis, normonatremic dehydration with absence of any evidence of an ongoing infectious process. Her Anti Nucleic acid antibody (ANA) panel, Aldolase, Rheumatoid factor and Angiotensin-1-Converting Enzyme levels were unremarkable. Creatine kinase levels were near normal. Her Neopterin and LDH levels were significantly elevated. Imaging with MRI scan with multiplanar multisequence of bilateral lower extremities and Pelvis showed significant diffuse myositis and soft tissue swelling. The diagnostic criterion for Juvenile Dermatomyositis include: (1) the typical pathognomonic rashes, (2) elevated muscle enzymes, (3) symmetric proximal muscle weakness and neck flexors, (4) muscle biopsy characteristic of juvenile dermatomyositis, and (5) EMG findings characteristic of juvenile dermatomyositis. Having ruled out an infectious process a muscle biopsy was performed, which also was subjected to Electron Microscopic (EM) analysis as the patient did not have extremely high muscle enzymes, necessitating a muscle biopsy . Hematoxylin & eosin stained sections were compatible with inflammatory myopathy. Ultrastructural examination demonstrated myofiber size variability, frequent rounded atrophic fibers with myofibrillar disarray, internalized nuclei, and increased interstitial collagen deposition. Endomysial capillaries were decreased in number, but showed reactive endothelial changes. Some showed prominent endothelial tubuloreticular inclusions (Figure),characteristic of JD. In summary, absence of serologic and tissue evidence of any other inflammatory myopathy, offending pharmacotherapy, infectious disease and presence of imaging and tissue evidence (vascular injury and tubuloreticular inclusions) comprised the work up of a child with SCD with Dermatomyositis.

Management- Prompt treatment with prednisone (2 mg/kg/day), methotrexate (10 mg) weekly and monthly IVIG (2gm/kg/dose) infusions was started, once diagnosis was confirmed showing a dramatic clinical response. Prednisone was slowly tapered after 1 month of treatment. She showed gradual improvement in her symptoms, the strength in proximal muscle in both upper and lower limbs improved eventually to a point where the contractures in the elbows and knees improved and she started ambulating without support. Patient's Hydroxyurea was restarted at a low dose of 15mg/kg/day and increased to 20 mg/kg/day slowly, as her systemic symptoms of Dermatomyositis subsided.

Discussion- Working up a child with SCD who presents with sudden onset non weight bearing can be complicated. Vaso-occlusive bony pain crisis , Osteomyelitis , septic arthritis are common clinical scenarios, but an underlying rheumatologic illness in pediatric SCD patient mimicking a sickle cell pain crisis presents a unique diagnostic challenge one which, albeit has been reported in literature, but rarely includes electron microscopic ultrastructural examination as part of evidence and work up. This patient's relatively mild muscle enzyme elevation and Hydroxyurea therapy made the initial diagnosis more challenging. We present the first pediatric SCD patient with clinically and pathologically proven case of Dermatomyositis with EM evidence, highlighting a unique clinical scenario ,diagnostic challenges and management strategies.

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