Nasopharyngeal carcinomas (NPCs) account for less than 1% of all malignant tumors and affect about 1 person in 100,000 in North America and Western Europe. It is more common in Asia and North Africa, where it affects 5–9 people per 100,000 [5]. The undifferentiated pathological subtype is the most common, most often associated with paraneoplastic syndromes such as fever, leukemoid reactions, and osteoathropathy [6]. The combination of dermatomyositis and cancer is common, affecting 18–32% of patients [2]. However, its association with pharyngeal carcinoma is not well described. Most often it is associated with the undifferentiated type, somewhat less frequently associated with the differentiated type, and never with well-differentiated cancer [7]. It may be more severe than the consequences of the primary tumor itself and may precede, follow, or be concomitant with the diagnosis of cancer. This is the finding in our case where symptomatology was dominated by dermatomyositis.

The pathogenesis of dermatomyositis is still poorly known, and several mechanisms have been suggested. Two theories have been developed: hormonal theory and immunological theory. Hormonal theory hypothesizes that it is the tumor that secretes biologically active hormonal polypeptides that are homeostatically inappropriate. These polypeptides are thought to be responsible for different clinical endocrine syndromes [7]. In the immunological theory, paraneoplastic syndrome is the result of cross-reactions of antibodies produced against tumor antigens, with normal tissues having a similarity of structures [7].

The diagnosis of dermatomyositis is based on five criteria according to Bohan and Peter [8]: progressive, symmetrical muscle weakness of the neck girdles and flexor muscles; dermatological signs (heliotropic rash with periorbital edema; Gottron’s papules (scaly dermatitis on the joints of the fingers); dermatitis on the elbows, knees, and feet; and a muscle biopsy in favor of myositis.

An increase in serum muscle enzymes is indicative of muscle necrosis (especially CPK, aldolase, LDH). These are increased in 70–90% of patients, however a normal rate should not rule out the diagnosis [1]. An electromyographic profile in favor of muscle damage. The presence of three or four of these criteria, in addition to the rash, enables the diagnosis of dermatomyositis, and the presence of two criteria associated with the rash is very suggestive of dermatomyositis. Thus, faced with the progressive muscle weakness and elevation of LDH associated with the typical rash, we made the diagnosis of paraneoplastic dermatomyositis.

Dermatomyositis can be idiopathic, especially in children. However, it is usually linked to a malignant tumor, as shown in the epidemiological study by Hill et al., in which 32% of dermatomyositis were associated with cancers of the ovary, lung, pancreas, breast, gastrointestinal tract, or non-Hodgkin lymphoma [2]. Also, Chan published a series of dermatomyositis cases in Singapore, in which 41% were nasopharyngeal carcinomas [9]. In addition,a statistical study carried out in China found an association of dermatomyositis with cancer of 20.3%, of which 78.5% concerned nasopharyngeal carcinoma [10].

The treatment of dermatomyositis in a cancer patient involves treatment of both the dermatomyositis and the tumor. Treatment is the same in patients with or without associated cancer and aims to increase muscle strength and improve extramuscular manifestations. First-line treatment is based on high-dose corticosteroid therapy with the usual hygienic-dietary measures of corticosteroid therapy [11]. Before the use of corticosteroids, the prognosis of dermatomyositis was poor, with mortality of 50–60% [12].

Corticosteroids are prescribed at a dosage of 1 mg/kg/d for 4–8 weeks on average, until the regression of clinical signs and the reduction or normalization of muscle enzymes. Then, a progressive reduction can be initiated until the minimum effective dose is achieved for 6–9 months without relapse [13]. For severe forms of dermatomyositis, the use of intravenous bolus methylprednisolone at a dosage of 1 mg/kg/d for 3 d, then oral relay is recommended [12]. This was the case for our patient admitted in an altered state who received an injectable bolus and then oral relay. However, in the case of refractory or corticosteroids, other treatment options are used such as methotrexate, azathioprine, intravenous immunoglobulins, and rituximab [14].

In addition to corticosteroid therapy, treatment for nasopharyngeal carcinoma should be carried out. In stage I patients, treatment is exclusive radiotherapy of 70 GY at 2 GY/fraction over 35 sessions (5/week) as in our case.

The prognosis of nasopharyngeal carcinoma with dermatomyositis is the same as that of a nasopharyngeal carcinoma in general [10]. In addition, many authors have reported that a complete remission after radiation therapy on the tumor results in the disappearance or improvement of the symptoms and physical signs of dermatomyositis. Relapse of dermatomyositis was correlated with locoregional recurrence or the detection of metastases, therefore, a monitoring element after treatment of nasopharyngeal carcinoma should be undertaken.

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