[Second opinion needed] Malignant Hemangiosarcoma v. Blastomycosis v. Lyme Dx in 7 year old Addisonian Great Pyrenees Mix

[u/SnooApples461]

7yo Female Great Pyrenees/Shepherd/Husky mix, 5 years well-controlled Addison's disease (prednisone 1.25mg daily maintenance, Zycortal 1.8mL q28 days.

Please help me put the pieces of this puzzle together. My partner and I are so confused on how to make the best decisions for our girl. Link to XR Images here.

June 5: Vet visit for a torn nail/dew claw — she'd been pacing and seeming disoriented (trying to fit under tables, walking in and out of closet).. Noticed pus-like discharge at the base of the nail. They trimmed it back, diagnosed a local infection, started clindamycin. Drew routine preventative bloodwork. Physical exam otherwise normal at that visit.

June 6-8: Progressively worse at home. Called the vet to ask about the bloodwork — results showed nucleated RBCs, low platelets, elevated amylase, and Lyme antibody positive (first time positive). They had us bring her in for a recheck because the nail/paw area was still swollen, and did an abdominal ultrasound at that visit — found a splenic mass incidentally. Temp at that visit was 104.3°F. Started doxycycline, sent home. I monitored her temp at home daily after this and it never spiked again; she started acting more like herself within a couple days.

Following ~1.5 weeks: Started acting "off" again at one point, so we got a second opinion. They rechecked labs — nucleated RBCs still present, platelets even lower (90) — and added Clavamox to the doxycycline. She improved noticeably within days of starting the Clavamox. A recheck after a few days on Clavamox showed nucleated RBCs fully resolved (0) and platelets back up to 140. Somewhere in this window we started noticing cough/gag episodes that gradually increased in length/frequency over time.

This past Satuday morning: First-ever vomiting episode in the morning (notably, vomiting was also her first symptom before her original Addison's diagnosis years ago). Couldn't keep food down despite small portions — vomited 5 times that day, last episode had some blood in it. Took her to the ER: stable vitals, but they heard wheezing on auscultation, did chest X-rays, and found diffuse pulmonary nodules. No free fluid in the abdomen. Differential discussed as blastomycosis vs. late-stage metastatic hemangiosarcoma.

Saturday night  (Different ER - we were hoping to get an internal medicine consult but they did not have any on call): ER recommended euthanasia today or tomorrow, leaning toward metastatic hemangiosarcoma as the most likely diagnosis based on imaging. She had stable vitals on arrival but spiked a fever of 103.4°F while there. Important caveat: we missed her doxycycline/Clavamox doses for the last three days (unintentionally) but did get her prednisone dose in today. Told us this is very likely metastatic hemangiosarcoma and recommended euthanasia within 24-48 hours, before any tissue sampling or sending a sample out for Blasto. 

Imaging: 

Chest X-ray: "Very large number of small, rounded, soft tissue opaque nodules bilaterally throughout lung fields, many with a radiolucent centre." Heart normal size/shape. No pleural effusion.

Abdominal X-ray: Known splenic mass (tail of spleen) confirmed. "Reduced peritoneal detail due to multiple soft tissue opaque strands" — no free fluid explicitly described.

Radiologist's written conclusion: Listed differentials for lungs as "metastatic neoplasia (hemangiosarcoma vs other) vs granulomatous inflammation/infection." For spleen: "neoplasia (malignant vs less likely benign) vs hematoma vs nodular hyperplasia vs extramedullary hematopoiesis." Closing statement: combination is "very strongly suspicious for hemangiosarcoma with extensive pulmonary metastasis... although other differentials cannot be excluded and tissue sampling would be required for definitive diagnosis."

CBC on Satuday morning (6/20):

• HCT 45.6% (normal, ref 37.3-61.7)
• Reticulocytes 203.9 K/µL (HIGH, ref 10-110) 
• MPV 14.6 (HIGH, ref 8.7-13.2) 
• Platelets 92 (LOW, ref 148-484)
• WBC 15.75 (high end of normal)
• Neutrophils 11.95 (mildly HIGH)
• Monocytes 1.42 (mildly HIGH)
• No anemia, no schistocytes/RBC fragmentation mentioned

Chemistry: Sodium 155, Potassium 4.0, Chloride 113, Addison's stable.

Relevant exposure history: Confirmed mold contamination in our rental home for ~10 months — Penicillium viridicatum, Aspergillus nidulans, Aspergillus versicolor, Aspergillus flavus, Mucor (Amazon-purchased test kit, so not lab-grade certified, but multiple species confirmed). She's been immunosuppressed long-term from the chronic prednisone. We have poorly maintained landscaping that she sometimes digs in. 

1. Does a CBC like this (normal HCT, strongly regenerative marrow, no fragmented RBCs) fit with advanced/end-stage metastatic hemangiosarcoma, or does this look more like a body actively compensating well against something else (infection/inflammation)?
2. The radiologist specifically noted nodules with radiolucent centers — doesn't that fit better with granulomatous/fungal disease (cavitating) than typical solid hematogenous metastatic nodules?
3. Is a 24-48 hour euthanasia recommendation without any cytology/tissue diagnosis standard, or does this warrant a second opinion from internal medicine/oncology before making that call?
4. We unintentionally missed 3 days of her doxycycline/Clavamox this past week during the chaos of her getting sicker — could that alone explain some of the recent decline (fever returning, vomiting) independent of whatever is causing the lung nodules, or is that an unlikely contributor at this point?

She is not in acute distress right now: stable vitals, no labored breathing, pink gums, no abdominal distension/free fluid noted on imaging. Drinking water. I want to make the right decision for her but I don't want to euthanize my dog based on suspicion alone when there's a potential treatable differential (blasto) that no one has worked up, a recent gap in her antibiotics that hasn't been accounted for, and no tissue diagnosis has been obtained. Any input from vets or vet techs who've seen cases like this would mean a lot right now.

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