DISCUSSION

cPAN can affect all ages with the average age of diagnosis being 40-50 years old with a greater predominance in women [2]. The estimated prevalence is 31 cases in 1 million, and it is estimated that it accounts for 4% of all cases of polyarteritis nodosa [3]. In contrast to PAN, cPAN is limited to the skin and associated muscles and joints surrounding the affected area [2]. Clinical signs include tender subcutaneous nodules typically affecting the lower limbs, which may progress to ulceration in 50% of the cases [1]. Other dermatological features include livedo reticularis, livedo racemosa and purpura [1]. Late- stage features are necrosis, neuropathy, myositis and neuritis [1]. cPAN can be distinguished from sPAN by its lack of systemic involvement, hypertension, bullae, livedo reticularis gangrene of extremities, leucocytosis and eosinophilia [2]. Unlike PAN, it is not fatal if left untreated but follows a benign course that may either become chronic or relapsing and remitting over several years [1]. Multiple associations with cPAN include group A beta haemolytic streptococcus infections, hepatitis B and C, inflammatory bowel disease, CMV, parvovirus B19, tuberculosis, malaria, and drugs such as minocycline, sulphonamides and IV amphetamines [1, 2]. An incisional biopsy to deep fat for histopathology is mandatory to establish the diagnosis, as well as tissue biopsy for microbial culture depending on the clinical context. Differential diagnoses for other forms of small to medium vessel vasculitis include lymphocytic thrombophilic arteritis, panniculitis, venous thrombosis and atypical infection. Further investigations should include; cryoglobulins, ANA, ANCA, RF and complement levels to exclude secondary causes [1-2, 4]; and; imaging to exclude systemic organ involvement. There is no consensus on initial treatment, dosage, length of treatment, or specific drug combination [5, 6]. Current studies have noted that mild cPAN can be adequately treated with NSAIDs, colchicine, topical corticosteroids, and low dose corticosteroids [1, 4, 6]. The presence of ulceration in the initial episode predicts an increased risk of relapse and is associated with a worse prognosis [7]. In such patients, case series have demonstrated up to 1mg/kg/day of prednisone was associated with a significant reduction of pain, disappearance of subcutaneous nodules and significant improvement of cutaneous ulcers [1, 8]. For patients who were refractory to prednisone, the addition of IV cyclophosphamide, azathioprine and IVIG have been shown to induce remission [5-6, 9]. Studies have also advised for aggressive treatment for patients who had constitutional symptoms, severe course of disease or high acute phase reactants [5, 6]. Studies have found that a flare of cPAN usually follows attempts to wean prednisone [8]. Steroid sparing agents include colchicine, hydroxychloroquine, methotrexate, sulphapyridine, pentoxifylline and dapsone [1, 4-5]. Patients with cPAN should be followed up twice yearly and have regular surveillance to exclude possible progress to systemic PAN [1]. The likelihood of cPAN progressing to sPAN is rare. In a large case series examining 79 patients with cPAN there was no progression to systemic PAN in a follow-up period of up to 30 years [8]. However, a case series noted that patients have developed sPAN up to 19 years after the initial diagnosis [10].