Can a Lupron (leuprolide) injection cause a knot at the injection site and hip pain 3 months after administration?

Lupron Injection Site Reactions and Hip Pain at 3 Months Post-Administration

Yes, a Lupron (leuprolide acetate) injection can cause a persistent knot at the injection site and hip pain 3 months after administration, as localized reactions including induration and abscess formation are documented adverse events, and musculoskeletal symptoms including joint pain are recognized side effects of this medication. 1

Injection Site Reactions

Localized injection site complications are well-documented with Lupron:

• The FDA drug label explicitly lists "localized reactions including induration and abscess" as reported adverse events at the injection site during postmarketing surveillance 1
• A documented case report describes muscle fibrosis developing after Lupron injection, with the patient experiencing swelling, muscle pain at the injection site, and impaired walking ability 2
• Injection-site granulomas from leuprolide acetate have been reported, consisting of giant cells and granulomatous changes that can persist as palpable subcutaneous nodules 3

The "knot" you're experiencing could represent:

• Induration (hardening) at the injection site 1
• Muscle fibrosis 2
• Granuloma formation from delayed-type hypersensitivity 3
• Abscess formation (though this would typically present with other signs of infection) 1

Hip Pain Association

Hip pain 3 months post-injection is plausible through multiple mechanisms:

• Joint pain is specifically listed as a musculoskeletal adverse reaction in less than 5% of patients receiving leuprolide acetate 1
• The FDA label documents "symptoms consistent with fibromyalgia (e.g., joint and muscle pain, headaches, sleep disorders)" as postmarketing adverse events 1
• If the injection was administered in the gluteal region or upper thigh, local tissue reactions could cause referred pain to the hip 2
• Bone pain is reported in 5% of patients, which could manifest as hip discomfort 1

Clinical Considerations and Next Steps

Evaluation of the injection site should assess for:

• Palpable mass or induration suggesting granuloma or fibrosis 2, 3
• Signs of infection (warmth, erythema, fluctuance) if abscess is suspected 1
• Range of motion limitations if muscle fibrosis is present 2

Important caveats:

• While these reactions are documented, they are relatively uncommon, so alternative causes of hip pain should also be considered 1
• The temporal relationship (3 months) is consistent with chronic inflammatory reactions like granuloma formation rather than acute injection complications 3
• Imaging (ultrasound or MRI) may be warranted if a persistent mass is palpable to differentiate between fibrosis, granuloma, or abscess 2, 3

Management approach depends on the specific finding:

• Persistent induration without infection may resolve spontaneously over time 3
• Symptomatic granulomas or fibrosis may require surgical excision if causing significant functional impairment 2, 3
• Any concern for abscess requires urgent evaluation and possible drainage 1