Vasculitis Presenting as Calf Pain With Muscle-Limited Involvement

Discussion. Vasculitides are a group of inflammatory conditions in which damage to the vessel wall can lead to life-threatening tissue and organ dysfunction. The diagnosis of vasculitis can be difficult because the presenting symptoms are often very generalized and nonspecific, and the diagnosis often requires biopsy of the affected organ.^1-3 Diagnosis can be further complicated by the fact that several medical conditions mimic vasculitis.³

The affected organs often can give clues to the type of vasculitis.¹ Our patient’s case was unique in that her only symptom was lower extremity pain and swelling, without systemic organ system involvement. Further investigation was considered with either computed tomography angiography of the abdomen or arteriography of the mesenteric or renal system, but given the lack of symptoms such as fever, weight loss, abdominal pain or angina, hypertension, renal insufficiency, hematuria, or proteinuria, we did not feel there was any indication. Furthermore, our patient desired a very conservative approach, and was even hesitant to get a muscle biopsy at first. Additionally, she required 2 tissue biopsies before a diagnosis could be reached. Vasculitis localized to a specific muscle without other systemic manifestations is rare, and very few cases have been reported in the literature.²

Our patient had a delay of diagnosis for months, as did many of the patients in published cases.² After a muscle biopsy revealed vasculitis, she was promptly placed on prednisone, 60 mg, for 1 month, which led to a prompt resolution of her symptoms. She was then tapered to 5 mg by month 6 and was continued at this dose for the next 6 months. At nearly 1 year after initiation of treatment, our patient’s vasculitis relapsed, and she again developed calf pain; the corticosteroid-sparing agent methotrexate was added to her regimen.

While many cases of muscle-limited vasculitis respond to corticosteroids alone, cases have been reported in which patients had relapse or systemic symptoms requiring corticosteroid-sparing agents such as azathioprine, cyclophosphamide, or methotrexate.^2,4

As illustrated by this case, the diagnosis of muscle-limited vasculitis can be extremely challenging. MRI can aid in the diagnosis by showing increased signal intensity in the affected calf muscles and subcutaneous tissue on fat-suppressed images, which indicates edema from an inflammatory process.^4-7 Moreover, MRI findings give clues as to which area of the muscle must be biopsied and also can guide response to therapy. All of the reviewed cases of muscle-limited vasculitis involve the lower extremities. Most often, the gastrocnemius and soleus muscles are involved.^2,4-7 MRI comparison images in one case report have shown decreased signal intensity after treatment.⁴

Although a rare diagnosis, muscle-limited vasculitis should always be included in the differential diagnosis of unexplained lower extremity pain. Because of the nature and complexity of its presentation, clinical vigilance and awareness of muscle-limited vasculitis is critical in order to provide a prompt diagnosis and to begin treatment as soon as possible.

References:

1. Blaes F. Diagnosis and therapeutic options for peripheral vasculitic neuropathy. Ther Adv Musculoskelet Dis. 2015;7(2):45-55.
2. Khellaf M, Hamidou M, Pagnoux C, et al. Vasculitis restricted to the lower limbs: a clinical and histopathological study. Ann Rheum Dis. 2006;66(4):554-556.
3. Suresh E. Diagnostic approach to patients with suspected vasculitis. Postgrad Med J. 2006;82(970):483-488.
4. Yang SN, Cho NS, Choi HS, Choi SJ, Yoon ES, Kim DH. Muscular polyarteritis nodosa. J Clin Rheumatol. 2012;18(5):249-252.
5. Ahmed S, Kitchen J, Hamilton S, Brett F, Kane D. A case of polyarteritis nodosa limited to the right calf muscles, fascia, and skin: a case report. J Med Case Rep. 2011;5:450.
6. Aoshima M, Fukuchi K, Tatsuno K, Ito T, Tokura Y. Ectopic adipose tissue with vasculitis in the calf muscle explaining systemic symptoms in leg-limited cutaneous polyarteritis nodosa. Acta Derm Venereol. 2016;96(1):142-143.
7. Nakamura T, Tomoda K, Yamamura Y, Tsukano M, Honda I, Iyama K. Polyarteritis nodosa limited to calf muscles: a case report and review of the literature. Clin Rheumatol. 2003;22(2):149-153.