An Unusual Manifestation of Adenocarcinoma of Lung - Skeletal Muscle Metastasis

Sharan Badiger & Siddarthkumar Chawath

Introduction

Lung carcinoma the most common malignancy worldwide, presents as a metastatic disease in majority of the cases. The most frequent sites of distant metastases are liver, adrenal glands, bones, and brain. Skeletal muscle metastasis is an unusual presentation of lung adenocarcinoma.

Case report

A fifty three year old male patient, labourer by occupation, beedi smoker for twenty five years, admitted to tertiary care hospital with pain and swelling over left arm, cough and expectoration for the past two months, accompanied with significant weight loss. There was no evidence of chest pain or haemoptysis. On local examination there was hard swelling over extensor compartment of left upper limb with mild tenderness, no loss of sensation and mild restriction of range of movements on flexion at elbow. Respiratory and other systemic examination was within normal results. Plain CT of thorax defined multilobulated lesion in right perihilar location in right middle lobe (Figure 1).

Figure 1: CT of Thorax: Well defined multi-lobulated lesion in right perihilar location in right middle lobe measuring 2.9 x 2.4 cm.

USG of left arm showed an irregular heterogenous soft tissue lesion noted within the triceps muscle with few areas of intra-lesional necrosis, MRI of left arm showed lobulated lesion in posteromedial aspect of mid and distal arm, involving triceps muscle, medial aspect of brachialis, encasing brachial artery, veins and median nerve (Figure 2).

Figure 2: MRI of Left arm: Well defined irregular lobulated enhancing T1 hypo intense, T2 and T2 flair hyperintense lesion in the posteromedial aspect of mid and distal arm.

PET scan showed enhancing nodular soft tissue lesion noted in middle lobe of right lung, 2.9 x 2.4 centimetres. Biopsy revealed metastatic adenocarcinoma. For further studies Immunophenotyping was done which showed negative for EGFR and ALK. Patient was treated with palliative RT, Pem-Carbo f/b Pemtrexed maintenance and recently 3# of Gemcitabine. The patient died of metastasis to brain within eight weeks of diagnosis.

Discussion

Lung carcinoma is a leading cause of cancer-related mortality. The most common sites of distant metastasis in lung carcinoma are brain, bones, the liver, and the adrenal gland¹. The most common tumours that cause skeletal muscle metastasis are tumours originating from thyroid, oesophagus, stomach, pancreas, colon, rectum, bladder, breast, ovary, and prostateand skeletal muscle metastasis of lung carcinoma was first reported by Fisher ER². Willis RA reported four skeletal muscle metastases in their autopsy series composed of 500 lung carcinoma patients³. Skeletal muscle metastasis is a rare occurrence for any tumour with a reported incidence lees than one percent^4-5. The most common sites of muscle metastasis are thigh muscles, iliopsoas, and paraspinous muscles⁶.

The mechanism of skeletal muscle metastasis is unclear. Despite its rich vascular blood supply and a large mass in the body, it is resistant to haematogenous metastases. Organs that are frequently metastasized, including liver, lung, and bone have rich capillary networks and blood supply. As a result of the muscle metabolism, substances such as lactic acid, free oxygen radicals, and low pH in the environment constitute an infertile medium for proliferating tumour cells. In addition, mechanical insults due to contractions, high tissue pressure, and widely alternating blood flow are also against the survival of tumour cells⁷.

There are several hypotheses proposed for skeletal muscle metastasis in lung carcinoma. The most widely accepted hypothesis is the haematogenous route. In this hypothesis, it is believed that tumour cells are formed through tumour embolism. Some authors suggested that skeletal muscle metastases might originate from abnormal lymph nodes found in the muscle. In a study by Bocchino M et al. 1754 lung carcinoma patients treated between 2007 and 2012 were analyzed and forty six (2.6%) had skeletal muscle metastasis⁸. Despite the variations between different studies in terms of the association between histological subtypes and skeletal muscle metastasis, forty patients in that study (87%) had non small cell lung carcinoma and six had (13%) small cell lung carcinoma. Among non small cell lung carcinoma patients, twenty four (60%) had adenocarcinoma. The most common initial manifestation of skeletal muscle metastasis is a pain. Pain can be accompanied by extremity swelling. The case presented herein also applied with pain and swelling. Diagnostic methods for skeletal muscle metastasis are not specific. Direct films usually show only soft tissue shadows. MRI usually reveals hypointense signal in T1 and hyperintense signal in T2. MRI is preferred to distinguish soft tissue metastasis from an abscess, sarcoma, and other conditions⁹, similarly; our patient had hypointense signal on T1 and the hyperintense signal on T2 series. The optimum treatment and prognosis of skeletal muscle metastasis from lung cancer is unclear. Depending on the clinical characteristics, treatment options include observation, surgery, chemotherapy and radiotherapy.

Conclusion

Lung carcinoma with skeletal muscle metastasis should be considered as a potential differential diagnosis in patients presenting with an intramuscular mass.

Acknowledgements

Authors acknowledge the immense co-operation received by the patient and the help received from the scholars whose articles are cited and included in references of this case report. The authors also acknowledge the authors/editors/publishers of all those articles, journals and books from where the literature for this case report has been reviewed and discussed.

References

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