Small cell carcinoma of the lung differential diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]: Associate Editor(s)-in-Chief: Eiman Ghaffarpasand, M.D. [2]

Overview

Depending on the presentation, lung cancer should be differentiated from other lung diseases such as pulmonary tuberculosis, lung abscess, and respiratory tract infection and autoimmune diseases affecting the respiratory tract. Once lung cancer is confirmed, small cell carcinoma should be differentiated from other non-small cell carcinoma based on histopathological findings.

Differentiating Small Cell Lung Cancer from other Diseases

Small cell lung cancer should be differentiated from other diseases causing cough, hemoptysis, and weight loss. The following are the differentials:

Organ System		Disease	Clinical Manifestations								Diagnosis				Other Features
			Symptoms							Physical Exam
			Onset	Duration	Productive Cough	Hemoptysis	Weight Loss	Fever	Dyspnea	Ascultation	Lab Findings	Imaging	Pulmonary Function Test	Gold Standard
Respiratory	Parenchyma	Lung cancer	Chronic	Years	+	+	+	+/−	+	Hoarseness	The following investigations may be helpful: Complete blood count (CBC) ALT, AST Calcium Alkaline phosphatase LDH Creatinine	Contrast−enhanced CT of chest and upper abdomen	Not specific	Tissue biopsy (sample should be sufficient for molecular testing)	Risk factor: Cigarette smoking Types Small cell lung cancer (SCLC) Non−small cell lung cancer (NSCLC)
		Interstitial lung disease	Chronic	Variable	−	+	+	−	+	Wheezing Crackles or velcro rales Inspiratory high−pitched rhonchi	The following investigations may be helpful: Hepatic function test Renal function test CBC Serological testing	Nodular, reticular or both pattern in chest X−ray CT in patients with diffuse pulmonary lung disease	Reduction in FVC, RV, FRC, TLC and FEV1 on spirometry FEV1/FVC normal or increase Lung volumes Diffusion capacity (DLCO reduced)	Lung biopsy when lab, imaging, and PFT has indeterminate result	Clubbing is common in asbestosis and idiopathic pulmonary fibrosis
		Tuberculosis (TB)	Chronic	More than 2 or 3 weeks	+	+	+	+	+	Pleural effusion Crackles Whispered pectoriloquy Decreased fremitus Rhonchi	Sputum acid−fast bacilli (AFB) smear may be positive Mycobacterial culture may be positive Molecular testing may be helpful	Reactivation of TB is observed as infiltration in the upper lobe in chest X−Ray In patients with HIV, Tb is observed as lobar infiltration, adenopathy, lung mass named tuberculoma, small fibronodular lesions, and/or pleural effusion on chest X−Ray CT can detect early nodal process	Decreased FEV1 Reduced FVC	Isolation of Mycobacterium tuberculosis from some secretion	Etiology: Mycobacterium tuberculosis Complications: Pneumothorax, bronchiectasis, pulmonary destruction and chronic pulmonary aspergillosis
Cardiac		Pulmonary hypertension	Chronic	More than 2 years	−	+	+	−	+	Hoarseness	The following investigations may be helpful: HIV serology Antinuclear antibody (ANA) Rheumatoid factor (RF) Anti−neutrophil cytoplasmic antibody (ANCA)	Enlargement of the central pulmonary artery and right heart in chest X−Ray Pulmonary artery systolic pressure can be estimated in echocardiography	Low levels of FEV1 Decreased FVC DLCO reduced	Mean pulmonary artery pressure more than 25 mmHg at rest	Chest pain Ascites Syncope Peripherial edema
Organ system		Diseases	Clinical manifestations								Diagnosis				Other features
			Symptoms							Physical exam
			Onset	Duration	Productive cough	Hemoptysis	Weight lost	Fever	Dyspnea	Ascultation	Lab findings	Imaging	PFT	Gold standard
Autoimmune		Wegener's disease (GPA)	Chronic	Months	+	+	+	+	+	Hoarseness Stridor Wheezing	The following investigations may be helpful: ANCA, P−ANCA, C−ANCA BUN Creatinine Complete blood count Urinalysis Lung biopsy	Nodules, pulmonary infiltrates, reticular margins, pleural opacities and cavities in chest X−Ray Nodules, cavities and stellate−shaped peripherial pulmonary in chest CT Bronchoscopy may be helpful	Low levels of DLCO Reduce lung volumes	Tissue biopsy	Nasal crusting, sinus pain, chronic rhinosinusitis, nasal obstruction and discharge in upper airway Saddle nose deformity Purpura in lower extremities
		Microscopic polyangitis (MPA)	Chronic	Variable	+	+	+	+	+	Hoarseness Stridor Wheezing	The following investigations may be helpful: ANCA positive BUN Creatinine Complete blood count Urinalysis	Cavitation, nodules, and alveolar opacities in chest X−ray Head and chest CT may be helpful Electromyography/nerve conduction study may also be helpful	Reduced lung volumes	Tissue biopsy	Nerve damage Rhinosinusitis Purpura involving lower extremities
		Churg−Strauss	Chronic	Variable	+	+	+	+	+	Wheezing Rales Rhonchi Expiratory sounds(related to asthma)	Peripherial eosinophilia In active phase CRP and erytrocyte sedimentation rate high Elevated IgE ANCA positive	Infiltrates in chest X−Ray Ground glass opacities, tree−in−bud sign and small nodules in chest CT	Lung volumes decreased FVC reduced FEV1/FVC ratio <70%	Tissue biopsy	Asthma Eosinophilia Rhinosinusitis

References

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