In a patient with a chest CT showing no mediastinal or hilar lymphadenopathy but fibrosis in both upper and lower lobes, and laboratory findings of normal parathyroid hormone, hypercalcemia, and elevated angiotensin‑converting enzyme, what is the most likely diagnosis and recommended diagnostic and treatment approach?

Sarcoidosis Without Lymphadenopathy: Diagnosis and Management

This clinical presentation—pulmonary fibrosis in upper and lower lobes, hypercalcemia with normal PTH, and elevated ACE—is highly suggestive of advanced pulmonary sarcoidosis (stage IV), and you should proceed with tissue biopsy to confirm the diagnosis before initiating corticosteroid therapy.

Most Likely Diagnosis

The constellation of findings points strongly toward sarcoidosis:

• Hypercalcemia with normal PTH combined with elevated ACE is classified as "highly probable" for sarcoidosis according to the 2020 ATS guidelines 1
• The abnormal vitamin D metabolism pattern (normal PTH with hypercalcemia) reflects granulomatous 1-α hydroxylase overexpression, producing excess 1,25-dihydroxyvitamin D 2
• Upper lobe fibrosis is listed as "probable" imaging evidence for sarcoidosis 1

The Absence of Lymphadenopathy: A Critical Nuance

The lack of hilar or mediastinal lymphadenopathy is atypical but does not exclude sarcoidosis. This represents either:

1. Advanced fibrotic stage (stage IV) where granulomas have burned out and lymph nodes have regressed
2. Radiographically occult sarcoidosis, which has been documented in the literature 2, 3

The research evidence confirms that sarcoidosis can present with normal chest imaging while still causing systemic manifestations like hypercalcemia 2. One case series documented a patient with markedly elevated 1,25-dihydroxyvitamin D, high ACE, and hypercalcemia whose chest CT was negative for lymphadenopathy, ultimately diagnosed via lymph node biopsy 2.

Diagnostic Approach

Step 1: Confirm the Biochemical Pattern

Verify the characteristic vitamin D metabolism abnormality:

• Normal to low PTH (already confirmed)
• Elevated 1,25-dihydroxyvitamin D (should be checked)
• Normal to low 25-hydroxyvitamin D

This triad is "highly probable" for sarcoidosis 1.

Step 2: Exclude Alternative Diagnoses

Before confirming sarcoidosis, you must rule out:

• Chronic beryllium disease: Order blood lymphocyte proliferation test 1
• Infections (TB, fungal): Obtain microorganism stains and cultures from any tissue sample 1
• Malignancy: The hypercalcemia pattern (elevated 1,25-dihydroxyvitamin D with normal PTH) argues against malignancy, but consider if constitutional symptoms present 4, 5
• IgG4-related disease: Check serum IgG4 levels and IgG4:IgG ratio 1
• Drug-induced sarcoid-like reactions: Review medication history for immune checkpoint inhibitors, anti-TNF agents 1

Step 3: Obtain Tissue Diagnosis

Despite the highly suggestive clinical picture, tissue confirmation is essential because:

1. The absence of lymphadenopathy makes this an atypical presentation
2. Alternative diagnoses (particularly infections and malignancy) carry different treatment implications and affect mortality
3. Histopathology guides long-term management decisions

Biopsy approach:

• If accessible extrathoracic manifestations exist (skin lesions, palpable lymph nodes, muscle involvement): Biopsy these first as they are lower risk 3
• For isolated pulmonary disease: Consider transbronchial lung biopsy or surgical lung biopsy to sample the fibrotic areas
• Look for non-caseating granulomas with perilymphatic distribution, compact epithelioid histiocytes, minimal necrosis, and negative microorganism stains 1

Common pitfall: The fibrosis may show "nodular hyalinized fibrosis representing healed granulomas" rather than active granulomas, which still supports sarcoidosis 1. Scattered multinucleated giant cells may be the only finding in burned-out disease.

Step 4: Additional Supportive Testing

While awaiting biopsy:

• BAL with CD4:CD8 ratio: Elevated ratio supports sarcoidosis but is not diagnostic 1
• PET scan: May reveal occult extrathoracic involvement (parotid uptake, bone lesions, extrathoracic lymph nodes) 1
• Ophthalmologic examination: Screen for uveitis (highly probable finding) 1
• ECG: Screen for cardiac involvement (AV block in young/middle-aged adults is probable for sarcoidosis) 1

Treatment Approach

Immediate Management of Hypercalcemia

Before starting corticosteroids, stabilize the calcium:

1. IV hydration with normal saline
2. Bisphosphonate therapy (zoledronic acid) if calcium >13 mg/dL or symptomatic 4
3. Avoid vitamin D supplementation and calcium-containing products

Corticosteroid Therapy (After Tissue Confirmation)

Once sarcoidosis is confirmed and infections excluded:

• Prednisone 20-40 mg daily is the standard initial dose for symptomatic disease with hypercalcemia 6
• Monitor response with serial ACE levels and serum calcium: These should fall in parallel during treatment 6
• Transition to alternate-day regimen once calcium normalizes to minimize side effects 6
• Duration: Typically requires prolonged therapy (months to years) for fibrotic disease

Monitoring Strategy

Serial measurements every 2-4 weeks initially:

• Serum calcium
• ACE levels (useful for tracking disease activity during treatment) 7, 6
• Renal function (hypercalcemia can cause acute kidney injury) 2, 4
• Pulmonary function tests

Critical caveat: ACE levels are elevated in approximately 60% of active sarcoidosis cases but can be normal in some patients 7. Serial trends are more useful than single values 6.

Key Clinical Pitfalls to Avoid

1. Don't assume lymphadenopathy is required: Stage IV fibrotic sarcoidosis often lacks adenopathy 8, 2

2. Don't delay biopsy in atypical presentations: The absence of typical imaging findings increases the risk of alternative diagnoses like lymphoma or infection 2, 4, 5

3. Don't start corticosteroids before excluding TB and fungal infections: These can also cause granulomas with hypercalcemia and would be catastrophically worsened by steroids 1

4. Don't overlook extrapulmonary involvement: Check for cardiac, neurologic, renal, and ophthalmologic manifestations that may require specific monitoring or treatment 1

5. Don't ignore the possibility of coexistent hyperparathyroidism: Though rare, this has been reported and requires different management 6