Bell’s palsy misdiagnosis: characteristics of occult tumors causing facial paralysis

Many etiological factors can cause unilateral facial palsy but Bell’s palsy, is the most common diagnosis. In the report of 1989 patients presenting to a tertiary facial nerve center, Bell’s palsy accounted for 38%, acoustic neuroma resections 10%, cancer 7%, iatrogenic injuries 7%, varicella zoster 7%, benign lesions 5%, congenital palsy 5%, Lyme disease 4%, and other causes 17%. [6] There has been no report on the analysis of etiologies from a facial nerve reanimation clinic that mainly offers interventions to help restore a more normal appearance. The prolonged pattern of paralysis without recovery was the main complaint at our facial nerve reanimation clinic. Forty-two percent of the patients were diagnosed with facial paralysis associated with tumors, 26% with Bell’s palsy, 16% with trauma, 10% with infection and 6% with congenital anomalies. There was a significantly higher rate of tumors compared to results of previous reports [6].

Bell’s palsy is the most common cause of facial nerve paralysis or weakness and is typically self-limited. Bell’s palsy may be associated with mild pain, numbness, increased sensitivity to sound, and alterations in taste. Onset is usually rapid (< 72 h), with spontaneous recovery occurring within 2 to 8 weeks in more than 80% of patients. Although Bell palsy has a classic presentation readily identified with a thorough history and physical exam, it remains a diagnosis of exclusion after other potential causes are ruled out [7].

Facial paralysis of neoplastic origin is estimated to represent the etiology in approximately 5% of all cases [2]. Neoplastic origin may be neurogenic primary lesions of the seventh cranial nerve or secondary, extrinsic neoplasms [2]. We analyzed 9 patients with unilateral facial paralysis, all of whom had an initial diagnosis of Bell’s palsy and were ultimately diagnosed with occult neoplasms. The formal radiologic report of the initial MRI of the patients reported no evidence of tumorous lesions. We doubted the diagnoses of Bell’s palsy based on the unusual histories that were inconsistent with Bell’s palsy with respect to the progressive and irreversible unilateral facial paralysis in all patients. Persistent facial paralysis with no return of any function beyond 6 months is usually not idiopathic [8].

The diagnosis of Bell palsy based on the MRI findings in some situations may lead to a false sense of security for patients with unilateral facial paralysis. Despite the dramatic advances in technologies of the various diagnostic modalities, Jackson et al. wrote that there remain limitations of resolution, and false-negative results are not uncommon [9]. Surgical exploration of the facial nerve may serves as a diagnostic and therapeutic approach in selected circumstances [9]. Surgical exploration of the parotid gland and facial nerve should be considered in patients with facial nerve paralysis who show no signs of regeneration 6 months after the onset of paralysis and/or persistent electrophysiological signs of ongoing neuronal degeneration, even if imaging tests, such as MRI studies, show no evidence of tumor [2].

If the facial nerve paralysis progresses slowly to complete paralysis and persists without any sign of recovery, it strongly suggests a neoplastic lesion involving the facial nerve. A slow progression of facial paralysis is the clinical characteristic of the neoplastic disorder, in contrast with the typical brief and self-limited course of Bell palsy. Nevertheless, a sudden onset of facial paralysis does not always exclude tumor involvement of the facial nerve. Progressing unilateral facial paralysis beyond 3 weeks and no evidence of recovery after 6 months of paralysis strongly suggest neoplastic involvement in the facial nerve [1].

Pain was also the main associated complaint in our cohort (6 out of the 9 patients; 66.7%). Although facial pain is not unusual in patients with Ramsey-Hunt syndrome or Bell’s palsy, its presence must be investigated. Jackson and Glasscock [9] reported that pain was identified in 18% of their patients with facial nerve neoplasm. Persistent pain beyond several months after onset of facial paralysis should warrant further investigation for an occult neoplasm [8].

A cranial neuropathy other than the facial nerve is sometimes seen in patients with Bell palsy. However, a high level of suspicion is necessary when there are persistent sensory and motor deficits beyond the facial nerve [8] .

Previous treatment history of regional skin cancer is also known to be a strong causal factor for facial nerve paralysis, especially in patients with pain involving other nerves [8]. In our series, 3 of the 9 patients had a history of a regional skin squamous cell carcinoma.

In our cohort, the possible reasons for diagnostic delay were no abnormal findings on the initial image, nonspecific facial nerve enhancement on initial MR, or non-enhancement with gadolinium. Therefore, follow-up imaging with adequate coverage of the entire facial nerve and neuroradiology consultation appears to be an essential component to mitigate diagnostic delay. In our, patient 2 did not receive repeat imaging prior to surgery as no occult neoplasm was suspected. This patient was a 33-year-old-male with a typical history of right Bell's palsy. Quality and severity did not change over 8 months. At that time, there were only MRI report from other center (without consultation from neuroradiologist) and the report of MRI did not show any etiology. Four months later, he underwent reconstructive surgery after extensive consultation. The facial nerve was identified through a retrograde approach, and we found completely abnormal and infiltrative tumor invading the facial nerve. It was small but very hard mass arising from deep to the facial nerve extending into the parapharyngeal space. The final diagnosis was high-grade adenoid cystic carcinoma measuring at least 2 cm in size, with perineural infiltration and microscopically positive margin. After surgery, he received adjuvant radiation treatment. This would be an example of the occult neoplasm identified by consulting a neuroradiologist or repeating MRI images.

None of the nine patients would have been confirmed to have a neoplasm without rigorous and long-term follow up. Therefore, careful and deliberate follow-up incorporating appropriate imaging evaluated by expert radiologists is essential when confronted with atypical presentations of facial paralysis.

The approach to re-animation is especially challenging for these patients because of the diagnostic dilemma coupled with limited options due to their late presentations. In our study, seven out of the 9 patients (77.8%) underwent at least one type of facial reanimation surgery. Three out of the five (60%) patients were graded as HB III with satisfactory symmetry, mouth angle excursion and eye protection. Even in patients with occult neoplasms and those alive with disease, facial reanimation surgery an improve quality of life in selected patients.

The limitations of this study were that because of the low number of patients with occult neoplasms making strong recommendations  should be done with caution. The source of initial HB grade may not be accurate because of the retrospective nature of this study.

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