What is the most likely diagnosis for a patient with IBD-like features, ascites, bulky ovary, myositis, and failure to respond to methylprednisolone?

Ovarian Malignancy with Paraneoplastic Myositis is the Most Likely Diagnosis

In this young woman with bulky ovary, ascites, progressive proximal myositis unresponsive to high-dose corticosteroids, and IBD-like gastrointestinal features, ovarian cancer with paraneoplastic myositis should be the primary diagnostic consideration. The constellation of findings—particularly the combination of pelvic mass with ascites and steroid-refractory myositis—strongly suggests malignancy-associated myositis rather than primary inflammatory myopathy or IBD-related complications.

Key Diagnostic Features Pointing to Malignancy

The Bulky Ovary with Ascites

• A pelvic mass with ascites in a young woman is ovarian malignancy until proven otherwise, regardless of other systemic manifestations
• The presence of ascites with an ovarian mass significantly elevates the probability of malignancy and requires urgent gynecologic oncology evaluation
• Ovarian cancer is well-documented to cause paraneoplastic syndromes, including dermatomyositis and polymyositis 1

The Steroid-Refractory Myositis Pattern

• Failure to respond to high-dose pulse methylprednisolone is highly atypical for primary inflammatory myopathy and should immediately raise suspicion for paraneoplastic etiology 1
• Primary idiopathic inflammatory myopathies typically show at least partial response to high-dose corticosteroids within 2-4 weeks 1, 2
• Cancer-associated myositis characteristically demonstrates poor or absent response to immunosuppression because the underlying driver is the malignancy, not autoimmunity 1

The Clinical Progression Pattern

• The rapid progression from iliopsoas to lateral thigh muscles with bilateral involvement suggests an aggressive underlying process 1
• Paraneoplastic myositis often presents with more rapid onset and progression compared to idiopathic inflammatory myopathies 1

Why Other Diagnoses Are Less Likely

IBD-Associated Myositis

• While myositis can occur as an extraintestinal manifestation of IBD, it is exceedingly rare 3
• IBD-associated myositis typically responds to treatment of the underlying bowel disease and corticosteroids 3
• The presence of bulky ovary and ascites cannot be explained by IBD, making this diagnosis insufficient to account for the full clinical picture
• The normal inflammatory markers (ESR/CRP) argue against active IBD as the primary driver 1

IgG4-Related Disease

• IgG4-related disease can cause inflammatory pseudotumors and myositis, but typically shows elevated inflammatory markers 1
• IgG4-related disease generally responds well to corticosteroids, which contradicts this patient's steroid-refractory course 1
• The combination of ovarian mass with ascites is not a typical presentation of IgG4-related disease

Lymphoma

• While lymphoma can cause ascites and muscle involvement, the bulky ovary is more consistent with primary ovarian pathology
• Lymphoma-associated myositis would typically show systemic lymphadenopathy and constitutional symptoms
• The negative tuberculosis workup makes lymphoma less likely but does not exclude it

Critical Diagnostic Workup Required

Immediate Investigations

• CA-125 tumor marker should be obtained urgently, as it is elevated in >80% of epithelial ovarian cancers
• Pelvic ultrasound with Doppler to characterize the ovarian mass and assess for malignant features (solid components, septations, irregular borders, increased vascularity)
• CT chest/abdomen/pelvis to evaluate for metastatic disease and characterize ascites
• Paracentesis with cytology if ascites is present—malignant cells would confirm cancer-associated myositis 1

Myositis-Specific Workup

• Paraneoplastic antibody panel including anti-TIF1-γ (transcription intermediary factor 1-gamma), which is strongly associated with cancer-associated dermatomyositis 1
• Creatine kinase (CK), aldolase, AST, ALT, LDH to document degree of muscle inflammation 1
• MRI of thigh muscles to confirm myositis and guide potential biopsy site 1, 4
• EMG if diagnosis remains uncertain, though clinical picture is already highly suggestive 1

Rule Out Myocarditis

• Troponin I (not troponin T) to exclude myocardial involvement, as myositis can be associated with life-threatening myocarditis 1
• Troponin T can be elevated from skeletal muscle inflammation alone, whereas troponin I is cardiac-specific 1
• Echocardiogram if any cardiac symptoms or troponin elevation 1

Management Algorithm

Step 1: Urgent Gynecologic Oncology Referral

• The bulky ovary with ascites requires immediate surgical evaluation regardless of other findings
• Diagnostic laparoscopy or laparotomy with frozen section may be necessary for definitive diagnosis
• If ovarian malignancy is confirmed, tumor debulking is both diagnostic and therapeutic for paraneoplastic myositis 1

Step 2: Hold Further Immunosuppression

• Do not escalate immunosuppression until malignancy is excluded 1
• Further corticosteroids or steroid-sparing agents (methotrexate, azathioprine) will not help paraneoplastic myositis and may delay cancer diagnosis 1, 2
• The lack of response to methylprednisolone already indicates this approach is futile

Step 3: Supportive Care for Myositis

• Physical therapy to maintain function and prevent contractures during diagnostic workup 1
• Analgesics (acetaminophen, NSAIDs if no contraindications) for symptom control 1
• Monitor for respiratory muscle involvement or dysphagia, which would require hospitalization 1

Step 4: Definitive Treatment

• If ovarian cancer is confirmed, oncologic treatment (surgery ± chemotherapy) is the treatment for the myositis 1
• Paraneoplastic myositis often improves or resolves with successful cancer treatment 1
• If myositis persists after cancer treatment, then consider immunosuppression with IVIG or rituximab 1, 2

Critical Pitfalls to Avoid

Do Not Attribute Everything to IBD

• The presence of IBD-like features does not mean all manifestations are IBD-related 1
• Ovarian pathology and myositis require independent evaluation
• Patients with IBD can develop unrelated malignancies, and the immunosuppression used for IBD may increase cancer risk

Do Not Delay Ovarian Mass Evaluation

• Never assume an ovarian mass with ascites is benign or inflammatory in a woman of reproductive age
• Even if myositis improves, the ovarian pathology requires definitive diagnosis
• Delayed diagnosis of ovarian cancer significantly worsens prognosis

Do Not Pursue Aggressive Immunosuppression Without Excluding Cancer

• Escalating to cyclophosphamide, rituximab, or other potent immunosuppressants before excluding malignancy is dangerous 1, 2
• These agents can accelerate tumor growth and worsen outcomes in cancer-associated myositis
• The steroid-refractory nature should prompt cancer workup, not more immunosuppression

Do Not Overlook Myocarditis

• Myositis can be associated with fatal myocarditis, particularly when presenting acutely 1
• Any dyspnea, chest pain, or arrhythmia requires immediate cardiac evaluation
• Troponin I and echocardiogram should be checked even in asymptomatic patients with confirmed myositis 1

The IBD Features: A Red Herring or Concurrent Process?

Possible Explanations

• Paraneoplastic gastrointestinal manifestations of ovarian cancer can mimic IBD
• Concurrent but unrelated IBD that happens to coexist with ovarian malignancy
• Medication effect if the patient was on NSAIDs or other drugs that can cause enterocolitis
• The colonoscopic biopsies showing "IBD features" need expert GI pathology review to determine if they truly represent IBD or another process 1

Management Approach

• Do not treat presumed IBD with immunosuppression until cancer is excluded
• If GI symptoms are severe, symptomatic management with antidiarrheals, dietary modification, or aminosalicylates (if truly IBD) can be considered 1
• Definitive IBD treatment should be deferred until the ovarian pathology is addressed

Normal Inflammatory Markers: What This Means

• Normal ESR/CRP does not exclude myositis or malignancy 1
• Some patients with inflammatory myopathies have normal acute phase reactants, particularly in cancer-associated myositis 1
• CK and aldolase are more sensitive markers for muscle inflammation than ESR/CRP in myositis 1
• The normal inflammatory markers actually argue against active IBD as the primary problem 1